Appalachian National

Scenic Trail Pilot Survey

Appalachian National

Scenic Trail Pilot Survey

Stanley J. Zarnoch, J.M. Bowker, H. Ken Cordell,

Matt Owens, Gary T. Green, and Allison Ginn

United States

Department of

Agriculture

Forest Service

Southern 

Research Station

General Technical 

Report SRS–143
September 2011 

Southern Research Station 

200 W.T. Weaver Blvd. 

Asheville, NC 28804

Authors:

Stanley J. Zarnoch, Mathematical Statistician, U.S. Forest Service, 

Southern Research Station, Asheville, NC 28804; J.M. Bowker, 

Research Social Scientist, and H. Ken Cordell, Pioneering Research 

Scientist, U.S. Forest Service, Southern Research Station, Forestry Sciences 

Laboratory, Athens, GA 30602–2044; Matt Owens, Research Professional,

Gary T. Green, Assistant Professor, and Allison Ginn, Graduate Assistant, 

University of Georgia, Athens, GA 30602–2044.

Front cover photo: Forest Path by Dwight Nadig, istockphoto.com, 

digitally altered.

Back cover photo: An Appalachian Trail sign at an exit sampling site in 

the pilot survey area by Matt Owens.
Appalachian National

Scenic Trail Pilot Survey

Stanley J. Zarnoch, J.M. Bowker, H. Ken Cordell, 

Matt Owens, Gary T. Green, and Allison Ginn
ii

This report was prepared for the U.S. Department of the 

Interior, National Park Service in partial fulfillment of 

Interagency Acquisition Agreement R2490050022 between 

the National Park Service, the Appalachian National Scenic 

Trail, and the U.S. Forest Service, Southern Research 

Station.

We are very grateful to many people for donating their time 

and effort to support this project. Volunteers assisting with 

pilot study field interviews were Joe Brookreson, Susan 

Brookreson, Donna Brother, Bob Cave, Polly Cave, Jessica 

Compton, Bob Fletcher, Jeannine Gaylor, Fran Huesman, 

Tom Johnson, Gale Kooser, John Roth, Dick Martin, Thyra 

Sperry, Kristi McKinley, Doris Morgan, Jean Neeley, Wendy 

Pacek, Dick Potteiger, Annie Powell, Barb Powell, Chelsea 

Powell, Ryan Sharp, Julie Strack, John Tatara, Barbara Van 

Horn, and Celeste Wiser. Also, thanks to Dave Winter of 

Leave No Trace Center for Outdoor Ethics for educational 

materials.

A number of local and regional Appalachian National Scenic 

Trail club members were instrumental in assisting with exit 

volume classifications for site days outside the pilot study 

region. These included: Laura Belleville, Scott Birchman, 

Dave Boone, Bill Boudman, Adam Brown, Julie Clemmons, 

Walt Daniels, Dave Field, Chris Firme, Jim Foster, Robert 

Freeman, Eleanor Grasselli, Dave Hardy, John Hedrick, 

Casey Horrigan, Tom Johnson, Mariah Keagy, Jim Lowe, 

Anne Maio, Howard McDonald, Gary Monk, Gail Neffinger, 

Andrew Norkin, Edward Oliver, Dan O’Neal, Dave Patrick, 

Jim Pelletier, George Ritter, Ron Rosen, Sara Sheehy, Julio 

Stephens, and Kerry Wood.

In addition, there were three trail clubs in the pilot survey area 

that warrant special recognition for their assistance throughout 

the course of this project. These include the Potomac 

Appalachian Trail Club, the Mountain Club of Maryland, and 

the Cumberland Valley Appalachian Trail Club. 

The Appalachian Trail Conservancy provided much needed 

assistance with logistics, contracting, and interviewing. 

Interviewers included Howard Crise, Dave Heath, and Sara 

Woll. Administrative personnel including Karen Lutz, Steve 

Paradis, Laurie Potteiger, Matt Robinson, and Bob Sickley 

merit special mention.

Many Federal agency personnel also donated substantial time 

and effort to this project. National Park Service employees 

providing considerable assistance included Rita Hennessey, 

Don Owen, Todd Remaley, Butch Street, and Pam Underhill. 

U.S. Forest Service employees providing much needed 

assistance included Don English, Marilyn Howard, Pete Irvin, 

Sue Kocis, and Shela Mou.

We thank numerous people who provided constructive 

reviews of an earlier draft, which includes J. David Reus, 

Steve Paradis, and Bob Sickley of the Appalachian Trail 

Conservancy; Lynne Seymour and Ashley Askew of the 

University of Georgia; Chris Siderelis of North Carolina State 

University; and Ray Souter of the U.S. Forest Service.

Finally, very special thanks is due Bob Gray (retired), 

formerly the National Park Service’s Chief Ranger on the 

Appalachian National Scenic Trail, for recognizing the 

need for such a study, obtaining the financial and political 

support, and ensuring that the study got off the ground.

Acknowledgments
iii

Contents

List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Part I—The Pilot Survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Sampling Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Estimation Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Databases and Computer Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Pilot Survey Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Part II—Trailwide Extrapolation (TWE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Sampling Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Estimation Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Extrapolation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Part III—Conclusions and Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Appendix A—List of Acronyms and Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Appendix B—The pilot survey prework spreadsheet consists of all the sites classified into

site-types and use-levels for the entire 2007 calendar year . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Page
iv

Table 1—The population of 120 sites in the pilot survey area from Harpers Ferry,

WV, to 10 trail miles north of Boiling Springs, PA, at the Scott Farm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Table 2—The total site days in each of the pilot study strata based on site-type and use-level,

the original designed allocation of the sample of site days for a.m. and p.m. sampling

(the actual achieved sample days in parentheses), and the total site days for the entire AT . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Table 3—The 2007 pilot survey sample calendar with 146 assigned sampling days along with

2 extra days [this does not include the special event at Boiling Springs, PA (June 2)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Table 4—The Boiling Springs, PA, shuttle bus tallies on June 2, 2007 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Table 5—Data files and SAS programs used in the pilot survey and trailwide extrapolation

to the entire AT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Table 6—The prework data file showing variable names, type, length, description, and

permissible values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Table 7—The day summary data file consists of 17 variables and 130 observations 

(the variables are currently in the file in this order based on the questionnaire, although a

reordering may be more appropriate for clarity) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Table 8—The individual interview data file consists of 43 variables and 1,233 observations

(180 were RETURN which were deleted) (the variables are currently in the file in this order

based on the questionnaire, although a reordering may be more appropriate for clarity) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Table 9—The estimated for each site-type and use-level using the design-based approach and

the model-based approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Table 10—The estimated for each site-type and use-level using the design-based approach and

the model-based approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Table 11—The estimated for each site-type and use-level using the design-based approach and

the model-based approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Table 12—The average clicker count per sample day for each stratum adjusted to a 12-hour

recreation day (this represents the average number of groups of all types of people exiting) . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Table 13—Augmented counts for the ATCH from 9:00 a.m. until 4:00 or 5:00 p.m. for the

pilot survey from June 1 to August 14, 2007 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Table 14—The monthly augmented counts, strata weights, weighted , , and estimates,

and standard errors for the Harpers Ferry augmented data under the model-based approach . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Table 15—Pilot survey visitation (site-type HF represents the summation over all use-levels and

all three sites because monthly augmented data were used) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Table 16—The final visitation estimates for the pilot survey and the trailwide extrapolation for

the entire AT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Table 17—The days when the ATCH Office in Harpers Ferry, WV, was officially closed or 

closed due to weather (some closed days had visitor counts because they were opened partially

or closed early due to bad weather conditions) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Table 18—Trailwide extrapolation visitation (site-type HF represents the summation over all 

use-levels and all three sites because monthly augmented data were used) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

List of Tables

Page
v

Figure 1—The Appalachian Trail is a 2,175-mile continuous trail across the Appalachian

Mountains from the summit of Mount Katahdin in Maine to the summit of Springer 

Mountain in Georgia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Figure 2—The pilot survey area from Harpers Ferry, WV, to 10 trail miles north of

Boiling Springs, PA, at the Scott Farm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Figure 3—A map of Harpers Ferry, WV, illustrating the intersection of the Appalachian Trail

with the town which leads to the development of the site-type Harpers Ferry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Figure 4—The survey questionnaire used to record information for each interviewed person

on a sample day. An additional question (1.4) was only asked when sampling at the 

Appalachian Trail Conservancy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Figure 5—The day summary form used to record information for each sample day. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Figure 6—The relationship of estimated and use-level for the five site-types using 

(A) the design-based approach and (B) the model-based approach. The circles represent the standard 

strata where TR = solid, P = long dash, and MU = short dash. The stars represent the augmented 

strata where HF = solid and ATCH = long dash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Figure 7—The relationship of estimated and use-level for the five site-types using 

(A) the design-based approach and (B) the model-based approach. The circles represent the standard 

strata where TR = solid, P = long dash, and MU = short dash. The stars represent the augmented 

strata where HF = solid and ATCH = long dash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Figure 8—The relationship of estimated and use-level for the five site-types using

(A) the design-based approach and (B) the model-based approach. The circles represent 

the standard strata where TR = solid, P = long dash, and MU = short dash. The stars 

represent the augmented strata where HF = solid and ATCH = long dash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

List of Figures

Page

Abstract

Visitation statistics on the Appalachian National Scenic Trail (AT) are 

important for management and Federal Government reporting purposes. 

However, no survey methodology has been developed to obtain accurate 

trailwide estimates over linear trails that traverse many hundreds of 

back-country miles. This research develops a stratified random survey 

design which utilizes two survey instruments, exit-site tallies and a 

survey questionnaire, to obtain visitation estimates on a portion of the AT. 

The design identifies three components (standard site days, augmented 

site days, and special events) which can be used to subdivide the 

sampling frame into estimator types that lead to more efficient sampling 

and estimation processes. In addition, design-based and model-based 

approaches are used to obtain estimates for comparison purposes.

The survey was performed from June 1 through August 14, 2007, on 

a 109-mile stretch of the AT from Harpers Ferry, WV, to 10 trail miles 

north of Boiling Springs, PA, at the Scott Farm. Visitation estimates were 

66,967 for the design-based approach and 70,912 for the model-based 

approach, with coefficients of variation of 23 and 16 percent, respectively. 

Individual strata-level visitation estimates were quite variable and differed 

substantially between the two approaches. 

An extrapolation to the entire trail for the whole year was performed by 

developing an appropriate sampling frame from which the strata weights 

could be obtained. Using the model-based approach and assuming the 

survey data were representative, the 2007 annual visitation extrapolation 

for the entire trail was 1,948,701 with a coefficient of variation of 20 

percent. 

Keywords: Design-based estimator, Lincoln-Petersen estimator, markrecapture estimator, model-based estimator, recreation trail use estimation.

Introduction

The Appalachian National Scenic Trail (AT) (see appendix 

A for a list of acronyms and abbreviations)is a continuous 

marked footpath extending more than 2,175 miles across 

the Appalachian Mountains from the summit of Mount 

Katahdin in Maine to the summit of Springer Mountain in 

Georgia (fig. 1). It forms a greenway that connects more than 

75 public land areas in 14 States. The AT was conceived in 

1921, completed in 1937, and established as the first National 

Scenic Trail by Congress with the passage of the National 

Trails System Act in 1968 (Appalachian Trail Conservancy 

2009). Consisting of over 250,000 acres that were acquired 

by the National Park Service (NPS) and the U.S. Forest 

Service (USFS), it is a component of the National Trails 

System and a unit of the National Park System.

Information on AT visitor use is important to help agency 

managers and planners identify where resources and funds 

should be utilized. In addition, the data serves as a valuable 

component of the NPS Public Use Data Collecting and 

Reporting Program whose objectives are (1) to design a 

statistically valid, reliable, and uniform method of collecting 

and reporting public use data for each independent unit 

administered by the NPS; (2) to enact a variety of quality 

control checks to eliminate errors; (3) to provide analysis 

and verify measurements of the public use data; (4) to 

assure consistency of data collection within units of the 

NPS; and (5) to support the continuous collection and 

timely publication of public use data (National Park Service 

2009b). Moreover, information is required so that each park 

unit can report annually on service-wide and park goals. For 

instance, the NPS Government Performance and Results Act 

goal examines visitor safety incidents in terms of 100,000 

visitor days. However, lacking a visitation survey, the AT 

administrators cannot accurately report to this important 

national objective.

Despite the need for such AT visitation information, a 

statistically valid, reliable, and uniform method of collecting 

and reporting public use data for any of the national trails 

has never been developed. Individual park and forest 

units, along with researchers, have collected some data on 

AT hikers and back-country users, particularly about user 

characteristics, attitudes, and preferences (Kyle and others 

2004, Manning and others 2000). In addition, use has 

been statistically estimated on some smaller trails which 

intersect the AT, like the Virginia Creeper Trail (Bowker 

and others 2004, 2007). However, there has never been 

a trailwide study of AT visitation. Several years ago the 

Appalachian Trail Conservancy (ATC) produced an estimate 

of 2 to 3 million annual visitors on the AT. More recently, 

the NPS (2009a) and the ATC (2009) report on their Web 

sites that estimated annual visits number between 3 and 4 

million. Unfortunately, documentation on the estimation 

methodology is not available and visitation was not 

categorized into day use, overnight use, nonrecreational use, 

or related categories. The ATC Web site also reports that 

thru-hikers have increased steadily over the past 5 decades, 

but have declined annually in number from 625 to 500 

between 2001 and 2007. While the information on thruhikers is likely accurate, they comprise an important but 

very small portion of overall AT use.

Appalachian National 

Scenic Trail Pilot Survey

Stanley J. Zarnoch, J.M. Bowker, H. Ken Cordell, 

Matt Owens, Gary T. Green, and Allison Ginn
2

The main objective of this study was to develop a pilot 

survey design for estimating AT visitation that can be 

used as a prototype for future estimates of visitation on 

the entire AT. The survey design and estimates would also 

provide measures of precision such as standard errors 

and confidence interval estimates. In addition, this would 

provide the basis for a survey design applicable to some 

or all of the other components of the National Trails 

System. A secondary objective was to use data from the 

pilot survey to develop a trailwide extrapolation (TWE) 

estimate that would provide a visitation estimate for the 

entire AT. Because of limited resources, the pilot survey 

was designed to collect data during a limited time (June to 

August) and spatial (109 miles) segment of the AT. Thus, 

any extrapolation to the entire AT had to rely upon several 

assumptions. A final objective of the overall study was 

to design a survey based on information from the pilot 

survey which would include the approximate cost and 

effort required to conduct a statistically rigorous future 

survey of the entire AT. Sampling variability, logistical 

considerations, and operational constraints obtained in 

carrying out the pilot survey were to be incorporated into 

this future survey design.

Part I—The Pilot Survey

Overview

The objective of the pilot survey emphasized the 

methodological development of an efficient sampling 

strategy for estimating recreation visitation on a linear 

hiking trail. Although it was important to obtain a good 

estimate of visitation for the survey, this was not the most 

important issue. A small pilot survey is often used as a 

precursor to a larger, more complete and complex survey 

in order to gather experience and necessary information 

about the sampling problems that are encountered while 

designing and implementing the survey. Completion of 

a pilot survey typically exposes unforeseen technical, 

logistical, and methodological problems, thus, facilitating 

increased efficiency in a subsequent larger survey. 

The pilot survey was applied to a 109-mile section of the 

AT extending from Harpers Ferry, WV, to 10 trail miles 

north of Boiling Springs, PA, at the Scott Farm from June 

1 through August 14, 2007 (fig. 2). This section provided 

a complex yet representative snapshot of the AT because 

it traversed multiple States and natural resource areas, 

intersected other low-use and high-use outdoor recreation 

sites, and was within easy traveling distance of major 

metropolitan areas. In addition, it was convenient to offices 

of study cooperators (NPS, ATC) and had a history of 

strong local club affiliations that would be beneficial when 

recruiting volunteers to assist with the field survey. The 

time period for the survey was selected to coincide with a 

period of expected high AT visitation which would provide 

maximum survey data for analysis, expose any unforeseen 

Figure 1—The Appalachian Trail is a 2,175-mile continuous 

trail across the Appalachian Mountains from the summit 

of Mount Katahdin in Maine to the summit of Springer 

Mountain in Georgia.
3

survey problems that needed to be addressed in future 

surveys, and coincide best with recruiting volunteers to 

administer the field survey. Information obtained from the 

pilot survey was later used to satisfy other objectives which 

included completion of the TWE to the entire AT by using 

appropriate strata weights and a preliminary design of a 

total AT survey.

The approach for the pilot survey uses onsite sampling of 

exit sites to obtain average daily estimates of the number of 

last-exiting recreationists (LERs) which are then expanded 

to the total annual visitation estimate. The methodology is 

based upon the concept that if all exit sites are identified and 

the number of LERs is counted for each day of the survey 

period, the sum will be the total visitation for that time 

period. The pilot survey design was based in part on the 

USFS National Visitor Use Monitoring (NVUM) Program 

that has been developed to obtain visitation estimates for the 

national forests across the United States (English and others 

2002, White and others 2007, Zarnoch and others 2002). 

Some trail-use studies have incorporated a stratified random 

sampling design based on trail segments rather than exit 

sites wherein trail users were counted as they passed using 

either visual or electronic means (Lindsey and Lindsey 

2004, Stynes 1996, Wolter and Lindsey 2001). However, 

by counting LERs, we ensure that only recreationists will 

be included in the visitation estimate and that recreationists 

will not be “double counted” because they are exiting the 

site for the last time and, hence, will not return and exit to 

be counted again. An alternative approach that should give 

similar visitation estimates is to count only first-entering 

recreationists. However, other information such as length 

of stay, satisfaction with the facilities, etc., was also desired 

from the AT survey and obviously could not be obtained 

from first-entering recreationists.

The true visitation can only be obtained by counting all 

LERs from all exiting sites on all days throughout the survey 

period. This would be a complete census (Jacobi 2003) and, 

although it gives the correct visitation, a census would be 

cost prohibitive to administer over virtually all dispersed 

recreation areas and back-country trails, especially for a long 

trail like the AT. Thus, a sampling approach that would be 

more feasible was used to obtain an estimate of visitation 

along with the standard error and confidence intervals.

The AT pilot survey was based on a stratified random 

sampling design (Cochran 1977) subsequently adapted 

to trail, wildland, and other recreation-use estimation 

(Bergstrom and others 1996, Bowker and others 2004, 

English and others 2002, Gregoire and Buhyoff 1999, 

Figure 2—The pilot survey area from Harpers Ferry, WV, to 10 trail miles north of Boiling Springs, PA, at the Scott Farm.
4

James and Schreuder 1971). The sampling frame consisted 

of the population of all possible recreation site days—a 

collection of all days at exiting sites that were open for 

recreation along the pilot survey area. These site days 

were then placed in 15 potential strata consisting of 5 

site-types and 3 use-levels. Within each stratum, a random 

sample of site days was selected which was visited by 

personnel who administered the onsite field survey. The 

main benefit of stratification was to reduce the standard 

error of the visitation estimate. Stratification also allowed 

a more controlled allocation of the sample throughout the 

population of site days and provided separate visitation 

estimates for each stratum which may be of interest for 

addressing various management issues.

Sampling Design

Sampling frame—The first step in the pilot survey, 

called prework, developed the sampling frame consisting 

of all site days along the AT from Harpers Ferry, WV, to 

10 trail miles north of Boiling Springs, PA, at the Scott 

Farm from June 1 through August 14, 2007. A site day 

was defined as any day that a given site was available for 

LERs to be exiting. The formation of the population of 

site days required the identification of all exit sites along 

the pilot survey area of the AT; i.e., where a recreationist 

would possibly exit the AT, though not cross country. This 

was accomplished by using a combination of resources 

including Geographic Information System data, trail maps, 

and guide books as well as interaction with AT personnel 

and other people knowledgeable about the trail. Table 1 

lists all 120 exit sites defined in the pilot survey area, giving 

their assigned site numbers, site names, and site-types 

(explained later). All sites were open for visitation during 

the pilot survey and, thus, each contributed 75 site days to 

the sampling frame implying a total of 9,000 site days.

The development of strata was based on site-type and uselevel applied to each site day. The objective was to formulate 

strata such that all site days within a given stratum were as 

uniform as possible with regard to AT visitation. Generally, 

when this is accomplished successfully in a stratified 

random sampling design, the average visitation between all 

the strata will be as different as possible and the variation 

within each stratum will be as small as possible (Cochran 

1977). This ideal situation is never met in practice, but if 

reasonably approximated, significant gains in precision 

of the visitation estimate are possible, resulting in smaller 

standard errors and narrower confidence intervals.

After reviewing the sites identified along both the pilot 

region and the whole AT, various patterns emerged that 

allowed the creation of several site-types. An exit site that 

simply consisted of a trail or road intersection across the 

AT was considered the trail/road (TR) site-type. If a parking 

lot was in the vicinity, as happened frequently where the 

AT intersected paved roads, then the site was a parking 

(P) site-type. It was presumed that both of these site-types 

would exhibit almost exclusive use by AT recreationists. In 

other areas there was a complex network of sites, some not 

clearly defined, with potential for considerable non-AT use. 

Examples of such included State parks through which the 

AT traveled for a considerable distance. These site-types 

were called multiple use (MU). There were also several 

AT sites identified that intersected Harpers Ferry, WV, a 

unique town and historical national park, which required the 

creation of a special site-type (HF). Here the overall AT and 

non-AT use were high and the intersection of the AT with the 

town was extremely complex (fig. 3) which did not resemble 

any of the other strata. The last site-type (ATCH) was unique 

to the pilot survey and consisted of the headquarters office 

of the ATC in Harpers Ferry, WV.

To further improve the stratification, the site days in each 

site-type were classified into one of three use-levels. These 

were low (L), medium (M), and high (H) depending on 

the anticipated number of LERs exiting from the site on 

the specific day. Note that this was based on the number of 

recreationists who were last exiting, not simply all exiting 

people, or people who were either passing through the site, 

or beginning an AT visit at the site. Also, these use-levels 

were specific to a given site-type. Thus, use-level L for 

site-type TR was different than use-level L for site-type 

MU. A simplified manner of referring to a given stratum 

is to combine the site-type and use-level. For instance, 

the stratum site-type TR and use-level L will be hereafter 

referred to as simply stratum TR–L. 

Stratification was formed by the classification of all site 

days into the 15 potential strata formed by the combination 

of the 5 site-types and 3 use-levels. For the pilot survey, 

there were no site days in the TR–H or ATCH–L strata, 

thus, resulting in only 13 strata. 

While performing the very time-consuming stratification 

of the site days with assistance from the ATC and local 

trail club staffs, it became evident that certain site days 

may have extremely high visitation due to special events 

in the vicinity. These site days were termed special events 

and were initially removed from the sampling frame. Here 

visitation was estimated in a different manner and added 

to the final visitation estimate. The only special event for 

the pilot survey was June 2, 2007, at Boiling Springs, PA, 

which was locally known as Foundry Day. The pilot survey 

sampling frame, thus, consisted of all site days for all the 

site-types (TR, P, MU, HF, and ATCH) from Harpers Ferry, 

WV, to 10 trail miles north of Boiling Springs, PA, at the 

Scott Farm during June 1 to August 14, 2007.

The well-known Mather Side Trail at Harpers Ferry, WV, 

was initially included in the sampling frame, but was later 

deleted for several reasons. First, it did not seem to fit into 

one of the five site-types previously defined. Although 

it most closely resembled site-type TR, it was felt that 

the proportion of LERs would be lower than the typical 

TR because it may contain a high proportion of non-AT 
5

Table 1—The population of 120 sites in the pilot survey area from Harpers Ferry, WV, to 10 trail miles north of Boiling Springs, PA,

at the Scott Farm 

Site 

number Site name 

Sitetype

0 HF ATC HQ ATCH

809 US 340 TR

810 (HF) VC shuttle parking HF

811 (HF) Shenandoah Street (20)a HF

813 (HF) Lower Town HF

814 C & O Canal Towpath E TR

816 Keep Tryst (12) P

817 Keep Tryst Road TR

819 Weverton Road (30) P

825 Gathland State Park S (60) MU

827 Gapland Road MU

828 Gathland State Park N (35) MU

829 Lambs Knoll Road N TR

832 Fox Gap (10) P

833 Reno Monument Road TR

834 Dahlgren Campground P

835 South Mountain Inn (40) (US40A) P

836 Dahlgren Chapel (15) P

838 Monument Road TR

839 Washington Monument Road MU

840 Washington Monument Road S (10) MU

841 Washington Monument Road N (40) MU

842 Washington Monument Road MU

844 Boonsboro Mountain Road (3) P

846 Boonsboro Mountain Road TR

848 Trail TR

849 US 40 Annapolis Rock (50) P

853 Thurston Griggs side trail TR

857 Blackrock Road TR

864 Wolfsville Road / MD 17 W (5) P

865 Wolfsville Road / MD 17 E (10) P

867 Trail TR

869 MD 77 TR

872 Warner Gap Road (1) P

874 MD 491 / Raven Rock Rd. TR

875 High Rock (22) P

878 Pen-Mar Road (40) MU

881 Pen Mar High Rock Road TR

884 Buena Vista Road TR

887 Old Route 16 TR

888 PA 16 (5) (resupply exit) P

890 Mentzer Gap Road (3) P

891 Mentzer Gap Road TR

893 Rattlesnake Run Road TR

897 Rattlesnake Run Road (4) P

899 Trail to P (40) TR

901 Rattlesnake Run Road (5) P

903 Old Forge Road (3) P

904 Trail, unknown TR

905 Snowy Mountain Tower Road (3) P

 

Site 

number Site name 

Site 

type

908 Swamp Road TR

909 Raccoon Run Trail TR

910 PA 233 (3) P

913 Access road TR

914 (CSP) US 30 / Trolley Trail MU

915 (CSP) Ramble Trail W MU

916 (CSP) Ramble Trail E MU

917 (CSP) Bridge / AT / Park Trail MU

919 W Parking (Chinquapin) neck MU

920 (CSP) Three Valley Trail MU

925 Stillhouse / Ridge Road Sandy Sod TR

926 Road, Methodist Hill TR

927 Middle Ridge Road TR

928 Hill Road TR

929 Dughill Trail TR

930 Ridge Road / Means Hollow TR

931 Milesburn Road TR

932 Ridge Road TR

933 Rocky Knob trail TR

934 Fegley Road TR

935 Trail, unknown TR

937 Big Flat (12) P

938 Dead Woman's Hollow (3) P

942 Tumbling Run Game Preserve Road TR

946 Woodrow Road TR

948 Michaux Road W TR

949 Michaux Road E P

950 Old Shippensburg Road P

951 PA 233 (3) P

953 (PGF) Bendersville Road W MU

954 Store / Hostel / Intersection S MU

955 (PGF) Overnight / Dressing lot MU

957 (PGF) Old Railroad Bed Road (8) MU

958 Pole Steeple trail TR

959 Old Forge Road TR

961 Trail, unknown TR

962 Limekiln Road TR

963 Tagg Run TR

965 Pine Grove Road / Tagg Run (2) P

967 Hunters Run /PA 34 (10) Zeigler P

970 Road / Trash Can Alley (10) P

973 PA 94 TR

975 Old Sheet Iron Roof Road (6) P

981 Old Town Road TR

982 Trail (to possible campground) TR

984 Whiskey Spring Park Mason-Dixon Trail (8) P

987 Camp Tuckahoe trail TR

988 White Rock Trail TR

993 Gutshall, to P TR

994 Ledigh Road (10) P

995 Ledigh Road (5) P

998 (BS) Mountain Road MU

999 Butcher Hill Yellow Breeches Cr MU

1000 (BS) 1st Street, PA 174 MU

1001 (BS) Butcher Hill Road MU

1002 (BS) PA 174 E MU

1003 Trail, unknown TR

1004 PA 74 TR

1005 Lisburn Road (6) P

1007 PA 641 / Trindle Road (4) P

1009 Ridge Road TR

1010 Old Stonehouse Road TR

1011 Appalachian Drive TR

1015 US 11 TR

1016 Bernheisel Road (6) P

1019 Bernheisel Road (Scott Farm) TR

HF ATC HQ = Harpers Ferry, Appalachian Trail Conservancy Headquarters Office; ATCH = Appalachian Trail Conservancy Headquarters; TR = trail/road; VC = 

Visitor Center; HF = Harpers Ferry; P = parking; MU = multiple use; MD = Maryland State Road; PA = Pennsylvania State Road; CSP = Caledonia State Park, PA; 

Appalachian National Scenic Trail; PGF = Pine Grove Furnace State Park, PA; BS = Boiling Springs, PA. 

a Numbers in parentheses indicates the number of parking spots.

.

921 Locust Gap / Greenwd Furnace S MU

922 Locust Gap / Greenwd Furnace N MU

923 Hosack Run Trail TR

924 Ridge Road TR

AT =
6

Figure 3—A map of Harpers Ferry, WV, illustrating the intersection of the Appalachian Trail with the town which leads to the development of the site-type Harpers Ferry.
7

visitation from Harpers Ferry, WV. This would then bias the 

visitation estimate for the TR strata if the Mather Side Trail 

was included in the site-type TR. Second, double counting 

may result because many people from the Mather Side Trail 

also visit, and would, thus, be counted at the ATCH site-type. 

Thirdly, the ATCH site-type had counts for practically the 

entire year from an auxiliary source which would be more 

useful than counts from a sample of the Mather Side Trail 

site days. Thus, the Mather Side Trail will not be discussed 

or included in any tables, figures, and analyses in the rest 

of this report. In addition, the special event on June 2 at 

Boiling Springs, PA, was excluded because it was surveyed 

in a different manner and included five site days; i.e., all five 

exit sites within Boiling Springs on June 2. Thus, the total 

pilot survey sampling frame consisted of 8,995 site days 

distributed by site-type and use-level as shown in table 2. 

The TR–L stratum had the most site days, totaling 40 percent 

of the entire sampling frame. The next largest were P–L with 

20 percent and MU–L with 13 percent. Although these strata 

may represent low-exit volumes and, thus, low levels of 

daily visitation, they comprise 73 percent of all site days and, 

therefore, may have a large impact on the visitation estimate.

Standard and augmented sites—The sites identified 

on the AT are classified as either standard or augmented. 

The standard sites are those where no information about 

recreation visitation is available from any sources except 

the pilot survey itself. In contrast, augmented sites are 

those where information is available from an auxiliary 

source that could be used, alone or in conjunction with 

other information, to derive an estimate of recreation 

visitation. For example, one might have monthly traffic 

counts, but would need information on the percentage of 

vehicles that contained LERs and the average number of 

people per vehicle to arrive at an estimate of recreation 

visits. The pilot survey designated all TR, P, and MU 

Table 2—The total site days in each of the pilot study strata based on site-type and uselevel, the original designed allocation of the sample of site days for a.m. and p.m. 

sampling (the actual achieved sample days in parentheses), and the total site days for the 

entire AT a

Sitetype Uselevel 

Pilot 

survey 

total 

Allocated 

a.m. sample 

size 

(achieved) 

Allocated 

p.m. sample 

size 

(achieved) 

Allocated 

sample size 

total 

(achieved) 

AT 

totala

- - - - - - - - - - - - - - - - - - - - number of site days - - - - - - - - - - - - - - - - - - 

TR L 3,624 4 (4) 6 (8) 10 (12) 184,988

TR M 651 4 (3) 6 (6) 10 (9) 8,112 

TR H 0 0 (0) 0 (0) 0 (0) 9,490

P L 1,781 4 (4) 6 (7) 10 (11) 81,429

P M 689 5 (6) 10 (7) 15 (13) 19,140

P H 80 9 (8) 16 (12) 25 (20) 8,625

MU L 1,161 4 (4) 6 (3) 10 (7) 13,279

MU M 542 5 (5) 10 (10) 15 (15) 3,028

MU H 167 9 (7) 16 (14) 25 (21) 2,883

HFb L 156 1 (0) 3 (2) 4 (2) 791

HFb M 23 2 (2) 3 (2) 5 (4) 156 

HFb H 46 4 (2) 7 (8) 11 (10) 148

ATCH L 0 0 (0) 0 (0) 0 (0) 120

ATCH M 14 —c

 —c —c —c 2 (2) 157

ATCH H 61 —c —c —c —c 4 (4) 88

Totald e 8,995 51 (45) 89 (79) 146 (130) 332,434 

AT = Appalachian National Scenic Trail; TR = trail/road; P = parking; MU = multiple use; HF = Harpers 

Ferry; ATCH = Appalachian Trail Conservancy Headquarters; L = low; M = medium; H = high. a Does not include Foundry Day at Boiling Springs, PA, on June 2, 2007, which included 5 site days. b HF are the sites 810, 811, and 813 at Harpers Ferry, WV. c ATCH was sampled for approximately 7 to 8 hours each day so no a.m. and p.m. is indicated. d Mather Side Trail was originally in the sampling frame, sample calendar, and backup sample but was 

deleted from all of these. e In the original prework site 881 was site-type MU and the sample calendar was developed from this. 

However, later the site was reclassified as site-type TR which resulted in two more samples than planned in 

TR and two less in MU. 
8

site-types as standard and the HF and ATCH site-types as 

augmented.

Generally, it is beneficial to have as many augmented sites 

as possible because it can increase the efficiency of the 

survey when using supplemental information collected by 

other sources. This results in cost savings which allows 

additional sampling to be allocated to the standard sites, 

thus, increasing the sample size and reducing variability. 

In addition, the variances of the estimates associated 

with augmented sites where data collection is usually 

more intensive and better controlled are often much 

less than that of the standard sites, so the quality of the 

visitation estimates that include augmented sites is further 

improved.

Although augmented sites can be very advantageous, they 

may present a few difficulties. First, the identification 

of augmented sites may be difficult and often requires 

extensive interaction with field personnel who are familiar 

with the sites and know which management activities 

are being performed that may enable the site to be an 

augmented site. Second, the concept of an augmented 

site is often a vague and abstract concept that must be 

understood in order to optimally identify these sites. 

Third, individual augmented sites may require unique 

methods of estimation that add complexity to the 

sampling methodology. Despite these problems, the use of 

augmented sites has been found to be worth the additional 

effort in terms of cost savings and variance reduction 

(English and others 2003). 

Prework spreadsheets—The creation of the sampling 

frame and strata required the identification and strata 

characterization of all sites along the entire AT. This 

was initially performed for the pilot survey area and 

subsequently completed for the rest of the mid-Atlantic 

region, along with the New England, Virginia, and southern 

regions. Beginning with Springer Mountain, GA, and 

continuing to Mount Katahdin, ME, all sites were given a 

site number, a site name, and assigned a site-type. Overall, 

a total of 953 “unique” exit sites were identified with 849 

being open the entire year. 

The formulation of the sampling frame was a vital 

component of the pilot survey and was dependent on the 

prework spreadsheets. Data entry consisted of identifying 

one to several date spans (begin and end) for a given site 

such that the specified days of the week all had the same 

use-level as assigned to that date span. A “1” was entered 

for a day of the week if it had that use-level in the date 

span and a blank if not. If a holiday had the same use-level, 

then a “1” was also entered, if not, then a blank (detailed 

examples follow in the next paragraph). Five recognized 

holidays were presumed to affect AT visitation—Memorial 

Day, Independence Day, Labor Day, Columbus Day, and 

Thanksgiving. Although others like Christmas Day and 

New Year’s Day may attract increased visitation to the AT 

by some avid hikers, it was felt that due to possible adverse 

weather conditions and other social and cultural activities, 

their impact on AT visitation would not merit holiday 

status. 

Many sites had a simple use patterns. For example, at 

site number 809 all days of the year were use-level L, so 

only one date span was needed with “1” for all days of 

the week and the holiday (app. B). However, others sites 

had more complex patterns of use-levels. For instance, 

site number 810 required seven date spans to represent its 

use-levels. This site had one date span for the time period 

January 2, 2007, (102) to December 24, 2007, (1224) to 

represent use-level L for all 5 weekdays. However, two 

additional date spans were needed for the weekends from 

January 2, 2007, (102) to March 31, 2007, (331) and 

November 1, 2007, (1101) to December 24, 2007, (1224) 

where use-level was M. In addition, January 1, 2007, 

(101) was considered use-level H, so a separate date span 

had to be created because this was not one of the specified 

five holidays. The date span from April 1, 2007, (401) to 

October 31, 2007, (1031) was specified use-level H for 

only the weekends, but for December 25, 2007, (1225) 

to December 31, 2007, (1231) use-level H was given to 

all days of the week. All five holidays were considered 

use-level H and, thus, given the date span 101 to 1231 

with “1” for holiday only. Note that each holiday could 

have been specified individually or possibly specified in 

a previous date span, but for this situation it was simply 

easier to “bundle” them under one date span. Thus, there 

are many ways in which the use-levels could be specified 

for a given site which led to identical classifications for all 

days of the year.

Although the method presented for site classification may 

appear confusing at first, once grasped it is simple and 

efficient for data entry and analysis. To ensure data quality, 

edit checks were performed to verify that a given site had 

at most one use-level for a given day and at most only 

365 days open for recreation with use-level L, M, or H. 

Such errors are common, especially for those entering data 

using this method for the first time. The number of sites 

identified for each of the regions was New England = 239, 

mid-Atlantic (excluding pilot) = 319, pilot = 120, Virginia 

= 146, and southern = 129, for a total of 953. The Mather 

Side Trail site is not included. The percent of sites open 

every day of the calendar year for each of the regions was: 

New England = 67 percent, mid-Atlantic (excluding pilot) 

= 98 percent, pilot = 99 percent, Virginia = 100 percent, 

and southern = 86 percent, with the overall weighted 

average being 89 percent.

The creation of the prework spreadsheet for the site-type 

ATCH was based on the augmented site data obtained 

from the Appalachian Trail Conservancy Headquarters 

(ATCH) Office in Harpers Ferry, WV. According to 

personnel at the ATCH, their daily tally data consisted of 

one tally only for each person who came into the ATCH, 
9

so multiple enters/exits by the same individual were 

eliminated. The ATCH staff was obviously not included in 

the daily tallies. However, a delivery person who showed 

interest in the AT or asked questions may be included. 

Months were characterized based on their monthly 

average visitor tallies with use-level L being < 20, M 

being 20 to 60, and H being > 60. In certain months, 

the weekends had significantly higher visitation than 

their monthly average and, thus, were classified into the 

next higher use-level. This resulted in January 1, 2007, 

through March 30, 2007, being use-level L. The period 

from March 31, 2007, through April 30, 2007, was M on 

weekdays and H on weekends. All of May 2007 was M on 

weekdays and H on weekends and Memorial Day. Both 

June 2007 and July 2007 were H all month while August 

2007 and September 2007 were M all month. October 

2007 was M on weekdays and H on weekends. November 

2007 was M all month while December 2007 was L all 

month. Appendix B illustrates these data in prework 

spreadsheet format. 

Sample selection—The sampling frame for the pilot 

survey consisted of 8,995 site days from which 146 

sample days were selected randomly within the specified 

strata according to the sample allocation shown in table 2. 

Although proportional allocation (Cochran 1977) could 

have been used to determine the number of site days to 

sample per stratum, a more efficient method is Neyman 

(optimal) allocation which selects more site days from the 

strata that are larger and/or more variable (Cochran 1977). 

The prework that was done for the creation of the sampling 

frame provided the information on strata size (table 2). 

However, although a measure of absolute variability 

was not known, a relative measure was believed to be 

positively correlated with use-level, which was found true 

after sampling was completed. Thus, using the Neyman 

allocation approach an allocation pattern was created as 

shown in table 2.

The allocation for the pilot survey relied upon researcher 

judgment for the optimal way to use the limited labor and 

financial resources of 146 sample days and, thus, did not 

strictly follow Neyman allocation. The approach, again 

requiring considerable researcher judgment, was to get 

the best sample possible while adhering to the Neyman 

allocation principles of strata size and variability. All TR 

site days in all use-levels were believed to have very low 

visitation and, thus, low variability so all use-levels were 

assigned 10 site days which was considered the minimum 

acceptable sample size. The P and MU site days had the 

opportunity for higher visitation and higher variability, 

especially for use-levels M and H; so 10, 15, and 25 were 

allocated to their L, M, and H use-level strata, respectively. 

Although visitation on the HF site days was anticipated to 

be very high, there were relatively few site days in these 

strata, so following the Neyman allocation principles 4, 

5, and 11 were assigned to the L, M, and H use-levels, 

respectively. Note that this is less than the minimum of 10 

due to the limited resources issue and the low strata sample 

size. The ATCH site consisted of a total of only 75 site 

days, so only 2 and 4 site days were assigned to M and H, 

respectively. 

The survey design was based on a 6-hour interviewing 

period for each selected sample site day. Bowker and 

others (2004) used 4- or 8-hour periods depending on 

time of year. The USFS uses 6-hour periods for NVUM 

(English and others 2002, Zarnoch and others 2002). 

This 6-hour sampling period for the TR, P, MU, and HF 

site-types was allocated randomly with one-third in the 

a.m. and two-thirds in the p.m. This disproportionate 

sampling allocation was used to get a better estimate 

during the afternoon hours when exiting visitation was 

believed to be higher and when there would be a greater 

potential to obtain more interviews and, hence, more 

survey information. The visitation estimate was weighted 

accordingly. The ATCH site-type was open for visitation 

from 9:00 a.m. to 5:00 p.m. (4:00 p.m. on weekends), so 

the sampling period was not assigned to an a.m. or p.m. 

category. The sampling calendar (table 3) was developed 

by randomly selecting the allocated sample size from 

each stratum by using a custom-designed computer 

program. Backup sampling days were generated in case 

the scheduled ones from the sample calendar could not 

be followed for a variety of reasons, which occasionally 

occurred as shown in table 3. The sample sizes that 

were actually achieved for the strata during the pilot 

survey, accounting for missing sample days and backup 

substitutes, are shown in table 2.

Characterization of the pilot survey sampling days—

There were 146 sampling days scheduled for the pilot 

study, excluding the special event at Boiling Springs, PA 

on June 2, 2007. The number of these actually sampled 

was 114 for a 78.1 percent accomplishment rate. Of the 32 

days that were assigned and missed, 12 were completed 

by using the correct backup days while 2 were completed 

with ad hoc backup days. In either case, all 14 were of the 

same site-type and use-level as that of the originally missed 

sample day, preserving as much as possible the original 

sampling allocation. Of the 32 missed days, 18 were never 

replaced with backup days and, thus, the sample size 

was reduced from what was originally planned. Over the 

course of the survey, 2 extra sample days were taken—1 

was in stratum MU–H and the other in P–L. Thus, the total 

number of sample days completed by field personnel was 

146−18+2 = 130. This consisted of 51 different sites with 

each being sampled anywhere from 1 to 13 times over 

the course of the survey. Of this sample, 101 sample days 

resulted in at least 1 interview being obtained. Although on 

29 sample days there were no people observed, and, thus, 

no interviews, these sample days still provided valuable 

data because they represented zero visitation. 
10

Table 3—The 2007 pilot survey sample calendar with 146 assigned sampling days 

along with 2 extra days [this does not include the special event at Boiling Springs, PA 

(June 2)] 

Site

Sub(date) or 

extra day Day Month Day Time Interviews

816 P L Fri. 6 1 a.m. 5

836 P M Fri. 6 1 p.m. 4

963 TR L Fri. 6 1 p.m. 1

955 MU H Sat. 6 2 a.m. 21

921 MU L Sat. 6 2 a.m. 0

849 849 (Fri. 6/22) P H Sat. 6 2 a.m. 2

875 849 (Sat. 6/23) P H Sat. 6 2 a.m. 14

955 MU H Sun. 6 3 p.m. 28

810 HF H Sun. 6 3 p.m. 16

819 P L Mon. 6 4 a.m. 1

917 MU L Thurs. 6 7 a.m. 1

835 P L Thurs. 6 7 a.m. 0

999 MU H Sat. 6 9 a.m. 3

875 P H Sat. 6 9 a.m. 2

970 P L Sat. 6 9 p.m. 0

819 P H Sun. 6 10 a.m. 8

849 P H Sun. 6 10 p.m. 15

0 ATCH H Sun. 6 10 a.m. + p.m. 25

1000 MU M Fri. 6 15 p.m. 7

849 P H Fri. 6 15 p.m. 11

825 MU H Sat. 6 16 a.m. 3

955 MU H Sat. 6 16 p.m. 49

1000 1000 (Sat. 6/23) MU H Sat. 6 16 p.m. 12

849 P H Sat. 6 16 p.m. 20

832 P M Sat. 6 16 p.m. 5

937 849 (Wed. 6/20) P M Sat. 6 16 p.m. 5

810 HF H Sat. 6 16 p.m. 18

878 MU M Sun. 6 17 a.m. 4

819 P H Sun. 6 17 p.m. 6

849 P H Sun. 6 17 a.m. 18

841 MU M Mon. 6 18 p.m. 0

893 TR L Mon. 6 18 p.m. 0

937 P L Tues. 6 19 p.m. 1

819 P L Wed. 6 20 a.m. 1

825 MU H Sat. 6 23 a.m. 2

999 MU H Sun. 6 24 p.m. 6

836 P M Sun. 6 24 p.m. —

1000 Extra day MU H Sun. 6 24 p.m. 1

0 ATCH H Mon. 6 25 a.m. + p.m. 16

920 MU L Tues. 6 26 a.m. 13

994 P L Wed. 6 27 p.m. 0

1011 TR L Thurs. 6 28 p.m. 0

1015 TR M Thurs. 6 28 a.m. 1

878 MU M Fri. 6 29 a.m. 5

1000 MU M Fri. 6 29 p.m. 7

811 HF M Sat. 6 30 a.m. 15

917 MU M Sun. 7 1 a.m. 20

819 P H Sun. 7 1 a.m. 5

836 P M Sun. 7 1 p.m. 4

continued

SitetypeUselevel
11

Table 3—The 2007 pilot survey sample calendar with 146 assigned sampling days 

along with 2 extra days [this does not include the special event at Boiling Springs, PA 

(June 2)] (continued) 

Site

Sub(date) or 

extra day Day Month Day Time Interviews

810 HF H Sun. 7 1 a.m. 34

813 HF H Sun. 7 1 p.m. 40

903 P L Mon. 7 2 p.m. 0

811 HF L Mon. 7 2 p.m. 35

841 MU H Tues. 7 3 a.m. —

954 MU M Wed. 7 4 p.m. 10

849 P H Wed. 7 4 p.m. 12

875 P H Wed. 7 4 p.m. 0

832 888 (Sun. 8/5) P M Wed. 7 4 p.m. 2

811 HF M Wed. 7 4 p.m. 34

923 TR M Thurs. 7 5 p.m. 0

999 MU M Fri. 7 6 p.m. 6

849 P H Fri. 7 6 p.m. 12

949 P M Fri. 7 6 a.m. 0

921 MU L Sat. 7 7 p.m. 1 

999 MU H Sun. 7 8 p.m. 6

890 P M Sun. 7 8 a.m. 0

813 HF H Sun. 7 8 p.m. 58

842 MU L Mon. 7 9 p.m. —

841 MU H Tues. 7 10 p.m. —

901 P L Wed. 7 11 p.m. 0

881a TR L Thurs. 7 12 p.m. 0 

922 MU L Thurs. 7 12 p.m. 1

841 MU H Sat. 7 14 p.m. 19

919 841 (Thurs. 8/2) MU H Sat. 7 14 p.m. 4

917 MU M Sat. 7 14 p.m. 6

819 P H Sat. 7 14 p.m. 7

810 813 (Sun. 7/15) HF H Sat. 7 14 a.m. 46

813 HF H Sat. 7 14 a.m. 35

811 HF M Sat. 7 14 a.m. 20

833 TR L Sat. 7 14 p.m. 1

875 875 (Sun. 8/12) P H Sun. 7 15 a.m. 0

865 888 (Wed. 7/11) P M Sun. 7 15 p.m. 1

938 P M Sun. 7 15 a.m. 1

811 HF M Sun. 7 15 p.m. 41

810 HF L Mon. 7 16 p.m. 21

924 TR M Mon. 7 16 a.m. 0

841 MU H Tues. 7 17 a.m. 2

0 ATCH H Tues. 7 17 a.m. + p.m. 7

841 MU H Wed. 7 18 p.m. 7

809 TR L Wed. 7 18 a.m. 1

881a TR L Thurs. 7 19 p.m. 1 

934 TR L Fri. 7 20 p.m. 0

810 HF H Sat. 7 21 p.m. 40

841 MU H Sun. 7 22 p.m. 9

919 MU H Sun. 7 22 p.m. —

1002 MU L Sun. 7 22 p.m. 25

849 849 (Sun. 7/29)

b P H Sun. 7 22 p.m. 8 

817 TR L Sun. 7 22 a.m. 3

continued

Sitetype

Uselevel
12

Table 3—The 2007 pilot survey sample calendar with 146 assigned sampling days 

along with 2 extra days [this does not include the special event at Boiling Springs, PA 

(June 2)] (continued)

Site

Sub(date) or 

extra day Day Month Day Time Interviews

929 930 (Wed. 8/8) TR L Sun. 7 22 a.m. 0

987 TR M Mon. 7 23 a.m. 0 

841 MU H Tues. 7 24 p.m. 12

999 MU M Tues. 7 24 p.m. 3

920 920 (Sun. 7/29)

b MU L Wed. 7 25 a.m. 0 

919 MU M Wed. 7 25 a.m. 7

849 P M Wed. 7 25 a.m. 0

810 HF L Thurs. 7 26 a.m. —

933 TR M Fri. 7 27 p.m. 0

1015 TR M Fri. 7 27 p.m. 1

819 P H Sat. 7 28 p.m. —

875 P H Sat. 7 28 a.m. 25

810 HF H Sat. 7 28 p.m. 48

1015 TR M Sat. 7 28 p.m. 0

955 MU H Sun. 7 29 p.m. —

875 P H Sun. 7 29 p.m. —

844 P L Mon. 7 30 p.m. 1

0 ATCH H Mon. 7 30 a.m. + p.m. 11 

836 P M Wed. 8 1 p.m. 2

875 P M Wed. 8 1 p.m. 15

841 MU H Fri. 8 3 p.m. 1

838 829 (Mon. 7/16) TR L Fri. 8 3 a.m. 1

927 TR L Fri. 8 3 p.m. 0

917 MU M Sat. 8 4 p.m. 18

819 P H Sat. 8 4 p.m. —

875 P H Sat. 8 4 p.m. 2

950 P M Sat. 8 4 a.m. 1

811 HF M Sat. 8 4 p.m. —

925 933 (Tues. 8/7) TR M Sat. 8 4 p.m. 0

878 MU M Sun. 8 5 p.m. 7

819 P H Sun. 8 5 a.m. —

849 P H Sun. 8 5 p.m. 8

875 P H Sun. 8 5 p.m. —

813 HF H Sun. 8 5 a.m. —

963 TR M Mon. 8 6 p.m. 0

938 Extra day P L Mon. 8 6 p.m. 0

0 ATCH M Mon. 8 6 a.m. + p.m. 3 

841 MU H Tues. 8 7 a.m. —

811 HF L Tues. 8 7 p.m. —

0 ATCH M Tues. 8 7 a.m. + p.m. 16

841 MU H Wed. 8 8 a.m. 6

955 MU M Thurs. 8 9 a.m. 1

841 MU H Sat. 8 11 a.m. 5

919 MU H Sat. 8 11 p.m. 2

899 TR M Sat. 8 11 a.m. —

849 P H Sun. 8 12 p.m. 30

905 P M Sun. 8 12 p.m. —

813 HF H Sun. 8 12 p.m. 50

919 MU M Mon. 8 13 p.m. 0

841 MU H Tues. 8 14 p.m. 0

— = If interviews are missing, then this scheduled sample day was missed; P = parking; TR = trail/road;

 MU = multiple use; HF = Harpers Ferry; ATCH = Appalachian Trail Conservancy Headquarters; L = low; 

 M = medium; H = high. . a Was originally site-type MU but was later reclassified as site-type TR. b Not an official backup day but the site-type and use-level were appropriate.

SitetypeUselevel
13

The major reason for the missing sample days was limited 

resources available for field survey administration. The 

pilot study employed two full-time field surveyors and 

occasionally augmented them with two project surveyors 

(whose major responsibilities were other duties besides 

field surveying) and several volunteers. Many of the 

missed sample days were on days when the number of 

randomly selected sample days exceeded two and there 

were insufficient interviewers available to perform the 

surveys. 

Survey procedures—The actual implementation of the 

survey began with assigning each sample day to a trained 

field survey interviewer who performed the survey. The 

procedure consisted of a 6-hour onsite tally of all people 

that were potential recreationists who appeared to be 

exiting the site. Obvious nonrecreating people such as 

uniformed State and Federal park personnel were not 

included in the survey tally. As mentioned previously, 

the survey was scheduled to be either a.m. (8:00 to 2:00) 

or p.m. (2:00 to 8:00) but minor departures from the 

specific times occurred and were recorded and adjusted 

for appropriately. At eight of the MU sites exiting vehicles 

were tallied because the volume and nature of the exiting 

people were not conducive to a people tally. 

In addition, survey interviews were conducted on a random 

sample of groups that were exiting. The person interviewed 

was selected randomly from each group by asking which 

group member, aged 16 or older, had the most recent 

birthday. The goal was to interview as many groups as 

possible. Thus, at the use-level L strata all groups may 

have been interviewed while at the use-level H strata the 

sampling fraction may have been much lower. The main 

objective of the questionnaire was to interview only people 

who appeared to be using the AT for recreation and were 

leaving the AT for the day at the time of the interview. 

Exceptions to the exiting criterion occurred at augmented 

sites like Harpers Ferry and the ATCH, where interviews 

were at random. All interviewees were screened out with 

a series of initial questions and then asked another set 

of questions dealing with arrival time, hiking distance, 

frequency of previous visits, demographics, and a few 

other trip attributes (fig. 4). In addition, other people 

who did not meet these criteria were also interviewed 

to a limited extent to gather other information needed 

for the survey estimation process. The exiting people 

tally during the interviewing period was recorded which 

provided information on the distribution of exiting people 

throughout the survey day. At the completion of a survey 

day, the interviewer filled out the day summary form (fig. 

5) which contains information on the interview team, date 

and time of the survey, tally, and number of completed 

interviews. 

Estimation Methodology

Statistical background—The estimation methodology used 

to obtain estimates for the pilot survey requires a fundamental 

knowledge of several statistical concepts. The estimators 

for visitation are relatively straightforward; however, the 

computation of variances is usually not. In particular, the 

sampling design must be considered when computing 

variances of certain estimated calibrating parameters and 

quantities. Moreover, visitation estimators often consist of 

the product or ratio of other estimated variables, and their 

variances are complex equations. A general introduction to 

these statistical issues (Cochran 1977) is presented here.

The pilot survey is a complex stratified cluster sampling 

design that must be considered when obtaining variances 

of estimated quantities. The primary sampling unit (PSU) 

is the site day within a stratum and the secondary sampling 

unit (SSU) is the group interviewed on a given site day. 

If Y is a variable measured at the PSU level, then an 

estimator for the mean for a given stratum is the simple 

arithmetic mean

(1)

where

yi= the observed variable on sample day i

n = number of sample days 

An estimator for the variance (ignoring the finite 

population correction) is

(2)

When quantities are estimated at the SSU level, the 

clustering of the data within a sample day must be 

considered. If this is not done and the observations are 

viewed as a simple random sample and equations (1) and 

(2) used, then variances will usually be underestimated, 

standard errors will be too small, confidence intervals will 

be too narrow, and statistical tests will have inflated type I 

error rates. In such a situation, the ratio of means estimator 

should be used for clustered data and is defined as
14

Figure 4—The survey questionnaire used to record information for each interviewed person on a sample day. An additional question (1.4) 

was only asked when sampling at the Appalachian Trail Conservancy. (continued to next page)

sample day. An additional question (1.4) was only asked when sampling at the ATC.

NVUM / Appalachian Trail Visitor Use Study ATC 

OMB #0596-0110 Interviewer:______________________________

Date: ___ /___ / 2007 Site # ATC Type M / HF Site Name: 

______________________________ 

Q1: Hi. We are conducting a study for the National Park Service. Would you be willing to 

take a few minutes to participate in an interview? 

 _____ Yes (person agreed to be interviewed – read Introduction) 

_____ No (did not agree to be interviewed – politely stop interview and visually 

obtain answers to Q 10, 11, 19) 

If in group: “I need to select just one of you to complete this interview. To make sure the 

survey is random, which of you had the most recent birthday and is 16 or older?” 

(Direct all questions to this person) “Please take a moment and review the following 

information.” Important- Allow interviewee to read OMB Information. 

Q1.4: Did you arrive here via the Blue Blaze / Mather Side Trail? _____ Yes 

(ATC) _____ No 

 

If at Special Site / M (Q1.5 only): 

Q1.5: Did you use the Appalachian Trail today?

_____ Yes (continue to Q2) 

_____ No “We are only surveying people who are using the Appalachian Trail. 

 Thank you for your time.” (visually obtain Q 10, 11, 19) 
15

Figure 4 (continued)—The survey questionnaire used to record information for each interviewed person on a sample day. An additional 

question (1.4) was only asked when sampling at the Appalachian Trail Conservancy. (continued to next page)

Q2. Is the AT your primary or secondary reason for visiting this area today? 

 Primary ______ Secondary ______ 

Q3: Is the purpose of your visit to the Appalachian Trail for recreation?

 _____ Yes, recreation type answer (ex. hiking, bird-watching, etc. continue to Q4) 

_____ No, non-recreation (maintainer, volunteer, etc.) “We are only surveying people who 

are here for recreation. Thank you for your time.” (visually obtain Q 10, 11, 19) 

Q4: Are you leaving the AT for the day, OR will you return and continue on today? 

 _____ Leaving the AT for the day (continue to Q4) 

_____ Will return and continue on today “We are only surveying people who are exiting 

for the last time today. Thank you for your time.” (visually obtain Q 10, 11, 19) 

Q5: How did you arrive at the AT today?

Read: Personal vehicle ____ Bus____ Bicycle ____ Walking ____ 

 Other ____ 

Q6: When did you arrive at the AT for this visit?

 _____ Today: What Time? __________________ ( 24 hr.) 

 

 _____ Earlier: When? Date: _____/ _____/ 2007 & Time: ____________ ( 24 hr.) 

 

Q7: About how far did you hike on the AT today?

 1 mile or less _____ More than 1 but less than 5 miles _____ 

 5 or more but less than 10 miles _____ 10 or more miles _____ 
16

Q8: Not including this visit, about how many times have you visited this particular AT 

 site for recreation in the past 12 months? __________

Q9: Not including this visit, about how many times have you visited anywhere along the 

 AT for recreation in the past 12 months? __________ 

Q10: How many males and females are in your group today? 

 Male: _______ Female: _______ 

Q11: How many of those are less than 16 years old? Male: _______ Female:_______ 

Q12: How many continuous nights before today did you stay on the AT? ____________ 

Q13: On a scale of 1-10, with 10 being the most satisfied, how satisfied were you with this 

 visit to the Appalachian Trail? __________ 

Q14: On a scale of 1 – 9, with 9 being extremely crowded and 1 being Not at All Crowded, 

 how crowded did you feel on the Appalachian Trail on this trip? (circle one #) 

 Not at all Crowded | Slightly Crowded | Moderately Crowded | Extremely Crowded 

 1 2 3 4 5 6 7 8 9 

Q15: If you could ask Managers to improve one thing about the way people experience the 

Appalachian Trail, what would you ask them to do?

 ___________________________________________________________________ 

Figure 4 (continued)—The survey questionnaire used to record information for each interviewed person on a sample day. An additional 

question (1.4) was only asked when sampling at the Appalachian Trail Conservancy. (continued to next page)
17

Q16: Consider the food, fuel, lodging, equipment and other expenditures necessary for this 

visit. About how much did your group spend in total for this visit to the A.T? 

 (Note: “If your trip involves visits to multiple places, estimate only the share of spending 

for this visit to the AT”) $ __________ 

Q17: What is your home Zip Code? __________ (99999 if foreign) 

Q18: What is your age group? 16-20 21-30 31-40 41-50 51-60 61-70 71+ 

Q19: What is your Gender? M / F 

Q20: Are you Hispanic or Latino(a)? 

No_____ Yes_____ (Refused) _____ 

Q21: With which racial group(s) do you most closely identify? Please choose one or more. 

 ______ American Indian / Alaska Native 

 ______ Asian 

 ______ Black / African American 

 ______ Native Hawaiian or other Pacific Islander 

 ______ White 

 Clicker count (including this interview):__________ 

 ______ (Refused) End Interview Time: ____________________( 24 hr.) 

Figure 4 (continued)—The survey questionnaire used to record information for each interviewed person on a sample day. An additional 

question (1.4) was only asked when sampling at the Appalachian Trail Conservancy.
18

Figure 5—The day summary form used to record information for each sample day. 

 Appalachian Trail Visitor Use Study 

Interview Day Summary Form 

Complete this form at the end of the interview period.

Interview Team

Person conducting Interviews: __________________________________ 

 Person using clicker: __________________________________________

Date and Times

Date: ____/____/_2007_ Weather Conditions: ____________________ 

Site # __________ Site name: _________________________________ 

Time at start of interview period: ___________________ ( military ) 

Time at end of interview period: ___________________ ( military ) 

 Scheduled shift: 8 – 2 (Am) or 2 – 8 (Pm) 

 Break time (in minutes): _________________________ 

Figure 5—The day summary form used to record information for each sample day. (continued to next page)
19

 

 Is this a Substitute Sample Day? Yes No 

 If so, what was the Original site number / day? #______ ___/___/___07 

Daily Clicker Counts

Total clicker / tally count at the end of interview period: _____________ 

 Did you count: 

 _____ Exiting Hikers or _____Vehicles 

 (Vehicles are counted at sites 825, 828, 840, 841, 878, 919, 955 and 999) 

Index Estimate

 Number of vehicles in parking lot: Shift Start______ Shift End ______ 

Completed Interviews

Total Number of Surveys Completed at end of interview period: ________ 

Figure 5 (continued)—The day summary form used to record information for each sample day.
20

(3) 

where

yi = the sum of the observed variable for all observations

in cluster i

xi = the number of observations in cluster i

n = number of clusters sampled

The estimated variance (ignoring the finite population 

correction) is

(4)

A couple general variance calculating methods are used 

quite often in the pilot survey. One is the variance of the 

product of a constant k and a variable. In this situation

Qˆ

1 = kxˆ (5)

and the estimated variance is

Vˆ Qˆ ( 1 ) = k 2Vˆ( xˆ) (6)

The other is the estimated variance of the sum of two 

independent estimates

Qˆ

2 = xˆ + yˆ (7)

which is simply the sum of the estimated variances of each 

and is defined as

Vˆ Qˆ ( 2 ) = Vˆ( xˆ) + Vˆ(yˆ) (8)

Another complexity that is often encountered is the 

estimated variance for an estimate that is a product of 

several other estimates that are independent. Let the 

estimate be defined as the product of two estimated 

independent quantities as

Qˆ

3 = xˆyˆ (9)

An estimate of the variance (Goodman 1960) is

(10)

An extension to the product of three independent variables

(11)

is often needed and this could be derived as an extension of 

equation (10) as 

 (12)

Occasionally an estimator is the product of three 

independent variables, one of which is also a quotient 

of two independent variables where the denominator is 

correlated with one of the other product variables. This 

is an extremely complex situation. When this occurs in 

the pilot survey, the variance of the quotient variable is 

very small; thus, it is assumed to be a constant with zero 

variance. This then reduces to the variance of a product of 

two variables as in equation (9) and, thus, the variance is 

estimated using a slight modification of equation (10).

Two approaches were used for estimating the various 

calibration parameters for the visitation estimators in 

the strata. The design-based estimation approach is the 

traditional methodology where estimators are developed 

from the sample data from each stratum according to a 

cluster survey design as outlined in statistical references 

such as Cochran (1977). This is the optimal method 

provided sufficient sample data have been obtained. 

However, when resources are limited, as was the case in 

the pilot survey, a model-based estimation approach may 

be more appropriate.
21

In the current study, a mixed linear model is developed by 

pooling the data from all the strata. The fixed components 

of the model are site-type and use-level. The interaction 

is assumed negligible and, thus, excluded from the model. 

The clustering of the observations within the sample days 

is addressed by treating them as repeated measures with 

the variance components covariance structure, implying a 

common variance and zero covariance for the observations 

within a cluster. The estimated parameters from the 

model are used to obtain the strata means and variances 

which reflect a smoother relationship than those from the 

design-based approach. When sample size is small and the 

data is highly variable, this is an appealing property. The 

assumption of no interaction between site-type and uselevel seems reasonable and is a necessary tradeoff for the 

smoother relationship. When the assumption is not valid, 

then the design-based approach may be more appropriate. 

If interaction effects are put into the model, then the 

estimates are identical to the design-based approach, 

though the variances are slightly different.

Another advantage of the model-based approach is that 

it is possible to obtain estimates for strata that are not 

specifically represented in the sample data as long as their 

site-type and use-level are represented in the data. In this 

situation the design-based approach would have to use a 

more arbitrary method to obtain a pooled estimate. This is 

not a factor for the pilot survey because all 13 strata were 

represented with data, and both approaches may be used. 

However, the TWE required estimates for two strata that 

were not represented with the pilot survey data which gives 

additional support to using the model-based approach. 

Moreover, the model-based approach has the potential to 

yield smaller variances because the estimates are based 

on data from all strata and not just one stratum as in the 

design-based approach. Thus, for these reasons, the pilot 

survey examined both approaches and after evaluation, 

used the model-based approach for the final estimates. 

Pilot survey visitation estimator—Total visitation for the 

pilot survey from June 1 to August 14, 2007, is defined as

 VISITS = SS + AS + SE (13)

where

VISITS = the total number of recreation visits to the AT

 in the pilot study area from June 1 through 

August 14, 2007

SS = the total number of AT standard site visits

AS = the total number of AT augmented site visits 

SE = the total number of AT recreation visits from the special 

event sites at Boiling Springs, PA, on June 2, 2007

The determination of an LER was dependent on the 

site-type of the sample day. For site-types TR and P, 

any potential interviewee who refused to be interviewed 

was considered an LER. In contrast, for site-types MU, 

ATCH, and HF, a refusal was simply considered a missing 

observation. The rationale for this was that it was believed 

that refusals at site-types TR and P were most likely 

LERs because these site-types were generally in remote 

areas with few other activities besides hiking on the AT. 

However, at site-types MU, ATCH, and HF there was a 

much higher diversity of activities and the likelihood of 

being an LER or non-LER was indeterminate.

All three components are independent so the variance is

(14)

Each of the above three components requires a different 

estimation methodology which is now presented.

Standard site-type component—The standard site-type 

component consisted of all sites in the strata composed 

of the TR, P, and MU site-types and all three use-levels 

L, M, and H where they existed. The standard site-type 

component, which does not contain the TR–H stratum in 

the pilot survey, is estimated as

(15)

with estimated variance 

 

(16)

where

Nh = the total number of site days in stratum h 

 = the average proportion of exiting groups in stratum 

h that are LERs
22

 = the average number of groups of people (recreating 

or not) counted as exiting in stratum h

 = the average size of the LER group in stratum h

Vˆ(Ph ),Vˆ(Ch ), and Vˆ(Gh ) = the estimated variances

of , , and ,

respectively

Note that the index of summation does not include strata 

TR–H because it does not exist in the pilot survey and, 

thus, there are only eight strata.

To get an estimate for equation (15), each of the four 

components must be obtained and multiplied. The Nh 

are known constants and are obtained from the prework 

spreadsheet data (table 2) while the , , and are 

estimated from the interview survey data.

Let

nh = the number of sample days in stratum h 

mhi = number of groups interviewed on sample day i in 

stratum h

Phij = 1 if group j on sample day i in stratum h was an LER

= 0 elsewhere

Moreover, there are two types of groups that are recognized 

in the interview process—those that are LER and those that 

are not. Thus,

Let

ghij = the number of people in interview group j on sample

day i in stratum h for an LER group 

ga

hij = the number of people in interview group j on sample

day i in stratum h for any type of group (the 

superscript “a” refers to “all” groups)

Also, there are two types of site days—those which tally 

people and those which tally vehicles.

Let 

cP

hi = the number of people tallied exiting the AT from 

sample day i in stratum h during the 6-hour 

interview period 

cv

hi = the number of vehicles tallied exiting the AT from 

sample day i in stratum h during the 6-hour 

interview period

The survey data can be used to obtain a ratio-of-means 

estimator for defined as 

(17)

with estimated variance

(18)

This estimator considers the clustering of the data on a site-day 

basis. The estimators given in equations (17) and (18) are 

valid when the number of sample days in a stratum is evenly 

distributed in the a.m. and p.m. categories. However, as the 

sample allocation was one-third a.m. and two-thirds p.m., an 

appropriate weighting scheme was used. In addition, missed 

sampling days and sample days without interviews (and no phij) 

further distort the designed allocation. Thus, the weights used 

for a given stratum were obtained as the proportion of sample 

days containing at least one phij that were a.m. and p.m. For 

instance, in stratum P–H the original allocation was a.m. = 9 

and p.m. = 16 but the achieved was a.m. = 8 and p.m. = 12 with 

the number of sample days with at least one phij being a.m. = 7

and p.m. = 11. Thus, the weights used for stratum P–H were 

a.m. = 7/18 = 0.39 and p.m. = 11/18 = 0.61. The analytical 

equations based on these weights are quite complicated and 

will not be presented here. Practical calculation of these 

estimators was easily performed for the design-based and 

model-based approaches by using PROC SURVEYMEANS 

and PROC MIXED (SAS Institute Inc. 2004), respectively. 

To obtain the average daily tally , the arithmetic mean is 

used because the daily count data are not clustered. Thus, 

when the sample day is a vehicle tally, 

(19)
23

with variance

(20)

The estimators shown in equations (19) and (20) are valid 

when the number of sample days in a stratum is evenly 

distributed in the a.m. and p.m. categories. This was not the 

case in the pilot survey, so separate estimates for a stratum 

were computed for a.m. and p.m. using equations (19) and 

(20). The a.m. and p.m. were then combined by simply 

averaging which achieved the appropriate weighting and 

the variance was computed in the typical manner. 

The constant “2” in equation (19) expands the 6-hour 

tally to a 12-hour recreation day. Note that for the TWE 

no adjustment is used to calibrate the recreation day to a 

shorter length during the winter months. This is because 

the use-level for a site was defined on a day basis. 

However, if the use-level was on a density-per-hour basis 

then a day length adjustment would be needed.

Recall that at a specific site either people or vehicles may 

be tallied as outlined in the sampling protocol. Although 

only eight sites are vehicle tally sites and the others are 

people tally sites, the survey is based on interviewing 

groups and, thus, vehicle tallies are the appropriate unit. 

This is because the group is the sampling unit for the 

interviews but the tally of groups may be impossible to 

accurately obtain if noninterviewed groups that pass the 

survey spot are attempted to be tallied. For vehicle sites the 

group is easily tallied because it is contained in a vehicle. 

At people sites exiting groups of people may mix together 

causing tally problems. Therefore, it is imperative to 

convert all people tally sample days to vehicle tally days 

before using the estimator (19) and its variance (20). This 

conversion is defined as

(21)

In addition, note that the denominator in equation (21) is 

the average group size for all exiting groups for a specific 

day i in stratum h, which is used to convert the people 

count cP

hi to a vehicle count cvhi. This is performed on a 

sample day basis and yields the variable cv

hi directly from 

which the stratum mean and variance could be easily 

obtained using equations (1) and (2), respectively. This is 

preferred to using the average exiting all group size for the 

entire stratum in the denominator of equation (21) in which 

case the variable cv

hi would be a ratio of two variables. To 

obtain the variance of such a variable would require a more 

complicated equation that would include the covariance of 

the numerator and denominator. 

To obtain an estimator for group size, the ratio-of-means 

must again be used for clustered data, yielding

(22)

with estimated variance

 (23)

The estimators shown in equations (22) and (23) are valid 

when the number of sample days in a stratum is evenly 

distributed between the a.m. and p.m. categories. However, 

as mentioned previously, the sample allocation was onethird a.m. and two-thirds p.m., and this has to be taken into 

account by appropriate weighting in the estimation process. 

In addition, missed sampling days and sample days 

without interviews (and no ghij ) further distort the designed 

allocation. Thus, the weights used for a given stratum were 

obtained as the proportion of sample days containing at 

least one ghij that were a.m. and p.m. Thus, the weighting 

methodology described for was also used here. 

The standard site-type estimator equation (15) is obtained by 

substituting the quantities for Nh , from equation (17), 

from equation (19), and from equation (22) into equation 

(15). The estimated variance is found by substituting the 

corresponding variances from equations (18), (20), and 

(23) into equation (16).

Augmented site-type component—Site-type ATCH—The 

site-type ATCH augmented site data consisted of 75 daily 

visitor tallies at the ATCH Office in Harpers Ferry, WV, 

obtained from June 1 through August 14, 2007. This was 

combined with the estimates and obtained from the 6 

sample site days taken during the pilot survey at the ATCH. 
24

The ATCH was open for 8 hours during the week and 7 hours 

on weekends which was considered the entire day with respect 

to last exiting recreationists. Thus, no adjustment for day 

length of 7 or 8 hours or expansion to a 12-hour day was used.

The visitation estimate for the ATCH for the pilot survey is 

as follows. 

Let

Nh

= total number of days that the ATCH has days in uselevel h, (h=M,H), during the pilot survey

nh

= number of days the ATCH tallied visitors for stratum 

h, during the pilot survey

AShi

ATCH = the ATCH visitor tally on day i in use-level h

then, the average daily augmented site-type visitation tally 

in use-level h is the arithmetic mean

(24)

with estimated variance

(25)

Note that all 75 days were tallied and, thus, Nh = nh

 = 75 

and consequently the finite population correction is zero 

which results in the variance being equal to zero.

The visitation estimate for the ATCH for the pilot survey is 

defined as

(26)

where

ASATCH = total visitation estimate for the ATCH for the 

pilot survey

= the proportion of groups exiting the ATCH that are 

AT LER

 = the average group size for all groups exiting the 

ATCH

= the average group size for all AT LER groups exiting

 the ATCH

The and are estimated as described previously in 

equations (17) and (22) and is estimated in a similar 

ratio-of-means manner as

(27)

with estimated variance

(28)

where 

ghij

a = the number of people in interview group j on 

 sample day i in stratum h for any type of group 

mhi = number of groups interviewed on sample day i in

 stratum h

Note that in equation (26) the summation is only over the 

use-levels M and H.

The estimators given in equations (27) and (28) are valid 

when the number of sample days in a stratum is evenly 

distributed in the a.m. and p.m. categories. However, as 

mentioned previously, the sample allocation was one-third 

a.m. and two-thirds p.m., and this has to be taken into 

account by appropriate weighting in the estimation process. 

In addition, missed sampling days and sample days 

without interviews (and no ghij

a ) further distort the designed 

allocation. Thus, the weights used for a given stratum were 

obtained as the proportion of sample days containing at 

least one ga

hij that were a.m. and p.m. Thus, the weighting 

methodology described for was also used here.

The variance of estimator (26) is quite complicated because 

it is a product of a constant and three variables as well 

as a ratio of a dependent variable. To simplify matters, 

assume that is a constant, which is reasonable because 
25

its variance is quite small and it is highly correlated with . 

Then we have approximately

(29)

because 0 as shown in equation (25) which 

drops four terms out of the general variance equation (12), 

simplifying the variance to a product of only two variables 

and two constants.

Augmented site-type component—Site-type HF—The 

HF site-type consisted of the three sites located at Harpers 

Ferry (810, 811, and 813). Although these sites could 

have been sampled and visitation estimated similarly to 

the standard sites, it was more advantageous to utilize the 

official monthly NPS recreation visitation for Harpers 

Ferry National Historical Park as augmented site data1

(National Park Service 2008). This provided visitation 

estimates based on data for the total 75 days at Harpers 

Ferry which was considered superior to just visitation 

estimates derived from the 20 site days that were planned 

to be sampled by the pilot study. In addition, it provided 

data for the entire year which was also advantageous 

for the TWE. However, there were several limitations to 

using this augmented site data that had to be resolved. 

The reported NPS visitation included (a) both AT and 

non-AT visits, (b) was not stratified by use-level, and (c) 

was only available on a monthly basis. To resolve these 

problems required a monthly derived from weighting the 

individual three use-level estimates obtained from the pilot 

study for the site-type HF by the monthly strata weights 

obtained from the prework spreadsheet data. The weighted 

and variance were defined as

(30)

Vˆ(Pi) = NLi

2

V P ˆ( L ) + NMi

2 V P ˆ( M ) + NHi2 V P ˆ( H )

NLi + NMi + NHi ( )

2

(31)

1 Personal communication. 2008. Butch Street, Management analyst, U.S. 

Department of the Interior, National Park Service, Public Use Statistics Office, 

Denver, CO 80225.

where

 

= weighted monthly proportion of interviewed groups 

 that were AT LERs for month i for site-type HF

NLi = the total number of site days in month i for stratum 

 HF–L

NMi = the total number of site days in month i for stratum 

 HF–M

NHi = the total number of site days in month i for stratum

 HF–H

= proportion of interviewed groups that were AT 

 LERs for stratum HF–L

 

= proportion of interviewed groups that were AT 

 LERs for stratum HF–M

= proportion of interviewed groups that were AT 

 recreationists for stratum HF–H

( ), ( ) and ( ) = the estimated variances of 

, , and , respectively

The NLi, NMi, and NHi are referred to as strata weights and 

were obtained from the prework spreadsheets. The , , 

, and their variances were estimated from the pilot study 

survey data from only June 1 through August 14, 2007.

To convert the NPS people tally to group tally a similar 

weighted mean of all group size was computed as

Gi

a = NLiGL

a + NMiGMa + NHiGHa

NLi + NMi + NHi

(32)

V Gˆ i

a

( ) =

NLi

2

V Gˆ L

a

( ) + NMi

2 V Gˆ Ma

( ) + NHi

2 V Gˆ Ha

( )

NLi + NMi + NHi ( )

2 (33)

where

= average size of all groups for month i for site-type HF

NLi = the total number of site days in month i for stratum 

 HF–L

NMi = the total number of site days in month i for stratum 

 HF–M

NHi = the total number of site days in month i for stratum

 HF–H
26

The visitation for the pilot survey utilizes these monthly 

weighted estimates and the monthly NPS augmented sitetype visitation estimate and is defined as

(36)

where

k = 1 if i = 6 or 7 (June or July) and k = 14/31 if i = 8 

 (August) 

AS S

 = the augmented site-type visitation estimate for the 

 pilot survey for site-type HF

AS S

i = the official NPS visitation at Harpers Ferry, WV, 

 for month i, i = 6, 7, 8 

Note that in the above equation month 8 is multiplied by 

(14/31) to reflect that the pilot survey terminated on August 

14. Also, the variance assumes that the augmented sitetype visitation AS S

i is known without error, that is, has zero 

variance. 

The variance of the above estimator (36) is quite 

complicated because it is a product of a constant and three 

variables as well as a ratio of two correlated variables 

 and . To simplify matters, assume that is a 

constant, which is reasonable because its variance is quite 

small. Then we have approximately

 

(37)

because by assumption which drops four

terms out of the general variance equation (12), simplifying 

the variance to a product of only two variables and two 

constants.

Special event—The pilot survey identified Foundry 

Day at Boiling Springs, PA, on June 2, 2007, as the only 

special event on the pilot study portion of the AT. Foundry 

Day was chosen as a special event day because the 

celebration was known to draw thousands of visitors to 

Boiling Springs, potentially increasing use on the AT on 

that day to a level greatly exceeding the defined strata. In 

addition, Boiling Springs consisted of a complex of five 

sites (998, 999, 1000, 1001, and 1002) that intersected the 

 = average group size of all interviewed groups for 

stratum HF–L

 = average group size of all interviewed groups for 

stratum HF–M

 = average group size of all interviewed groups for 

stratum HF–H

( ) , ( ) , and ( ) = the estimated variances 

of , , and , 

respectively

Also required was the monthly average group size for AT 

LERs defined as 

Gi = NLiGL + NMiGM + NHiGH

NLi + NMi + NHi

(34)

V (Gi) = NLi

2

V Gˆ( L ) + NMi

2 V Gˆ( M ) + NHi2 V Gˆ( H )

NLi + NMi + NHi ( )

2 (35)

where

= average size of all groups for month i for site-type HF

NLi = the total number of site days in month i for stratum 

HF–L

NMi = the total number of site days in month i for stratum 

HF–M

NHi = the total number of site days in month i for stratum 

HF–H

= average group size of AT LER interviewed groups 

for stratum HF–L

 

= average group size of AT LER interviewed groups 

for stratum HF–M

= average group size of AT LER interviewed groups 

for stratum HF–H

( ) , ( ) , and ( ) = the estimated variances 

of , , and , 

respectively
27

town, resulting in unique sampling problems. Thus, due to 

these issues, it was felt that these site days did not fit the 

criteria of any of the 13 strata and, thus, it was identified as

a special event.

The methodology to estimate visitation at this special event 

followed the general concepts used for the other sites but 

with some modification. The special event estimator is the 

total number of AT recreation visitors in Boiling Springs, 

PA, on June 2, 2007, and is defined as

SE = PSE NGSE GSE (38)

with estimated variance

SE SE SE SE SE SE SE SE SE

SE SE SE SE SE SE SE SE SE

SE SE SE SE SE SE

SE SE SE SE SE SE

(39)

where

 = estimator for the total number of AT recreating 

visitors in Boiling Springs, PA, on June 2, 2007

 = the proportion of all groups interviewed that are AT

recreating groups

= the number of groups of visitors (AT and nonAT) in Boiling Springs, PA

= the average group size for AT recreating groups

Note that this approach deviates from the general 

methodology in that exiting people and vehicles are not 

used in the estimation process, and and were 

not based on the last-exiting criterion. These deviations 

were necessary due to the complex nature of the trail 

intersections in Boiling Springs.

The major difficulty was to obtain an estimate of ,

the number of groups in Boiling Springs on Foundry Day. 

Initial investigation indicated that many visitors came to 

Boiling Springs via shuttle buses operating out of a local 

high school. Although these groups represented a portion 

of , there were other groups that came in private 

vehicles or simply walked to town. However, if somehow 

those who used the shuttle buses could be identified 

during the interviewing process, then typical markrecapture methods used for estimating animal abundance 

(Seber 1982) could be used to estimate . This was 

accomplished by simply adding a question during the 

interview that asked if they used the shuttle buses.

The Lincoln-Petersen estimator is a simple mark-recapture 

estimator used for wildlife population size estimation. 

It consists of a two-sample process where animals are 

captured and marked in sample 1, and then a second 

sample is taken. The estimator is defined as 

(40)

with estimated variance

(41)

where

 = the Lincoln-Petersen estimate of population size

n1 = number of animals marked in first sample

n2 = number of animals marked in second sample 

m2 = number of animals recaptured in the second sample 

 that were marked in the first sample

Applying the Lincoln-Peterson estimator to Boiling 

Springs, PA, let the first sample be the groups that took 

the shuttle bus and the second sample be the groups 

interviewed in town during the interviewing process. 

Although the groups in the first sample were not physically 

“marked,” they could be detected in sample 2 by asking the 

additional question “Did you take the shuttle bus to town?” 

Thus, for this application, 

 = number of visiting groups in Boiling Springs, PA

n1 = number of groups that took the shuttle bus

n2 = number of groups interviewed in Boiling Springs, PA 

m2 = number of groups interviewed that took the shuttle bus
28

Although the shuttle bus count was based on people, it may 

be converted to groups to give

n1 = Cb

Gb

(42)

where

Cb = the total number of people that took the shuttle bus 

 = the average group size for those groups that took 

the shuttle bus

An estimator for the number of groups in Boiling 

Springs, PA, is obtained by substituting these quantities into 

the general Lincoln-Petersen estimator [equation (40)].

One component of the survey process at Boiling Springs, 

PA, consisted of shuttle bus tallies. The shuttle bus operated 

from 9:00 a.m. to 4:00 p.m. and transported people from 

the high school to the festivities in town. Survey personnel 

stationed at the school tallied 610 people being transported to 

town (table 4). However, the observer took a break between 

10:59 a.m. and 11:50 a.m. (51 minutes) and, thus, the tally 

does not include this interval. To estimate the number of 

people on the buses during the break, the average number 

of people per minute was determined for approximately an 

hour before and an hour after the break. The hour before 

the break included the 10:02 to immediately prior 10:59 (57 

minutes) bus tallies, totaling 191 people. The hour after the 

break included the 11:50 a.m. to immediately prior 12:50 

p.m. (60 minutes) bus tallies, totaling 94 people. The average 

people per minute is, thus, calculated as (191+94) / (57+60) 

= 2.44. The break was 51 minutes so the number of people 

during this interval is 51(2.44) = 124. Note that although 

the break with no tallies was 51 minutes, the interval used 

was defined to include the 10:59 a.m. to immediately prior 

to the 11:50 a.m. bus tally which totaled 33 people. This is 

analogous to the methodology previously used to obtain the 

hourly bus tallies. Thus, subtracting the number taken on the 

bus at the beginning of the break (10:59) from 124 gives the 

total number of unseen break bus people as 124−33 = 91. 

The total number of bus people is the sum of those seen on 

the buses plus those unseen people during the break, yielding 

Cb = 610 + 91 = 701.

The other survey component was the interviewing 

process. This was performed at two of the five sites (999 

and 1000) in Boiling Springs from 8:00 a.m. to 4:00 p.m. 

following the standard procedure with the addition of 

the extra question pertaining to the shuttle bus. A total 

of 26 groups were interviewed—with 12 using the AT for 

recreation, 10 not using the AT for recreation, and 4 refusing 

to answer the interview. Thus, the proportion of groups that 

used the AT for recreation was = 12 / 22 = 0.5455 with 

( ) = 0.0113 and n2 = 22. During this period there 

were m2

 = 2 groups interviewed that took the shuttle bus 

with their average group size being = 3.0 and, thus, 

using equation (42) n1

 = 701 / 3.0 = 233.67. For simplicity, 

ignore the variance and assume that n1

 is a constant. In 

addition, there were 11 groups interviewed that used the 

AT for recreation and for which group sizes were obtained, 

yielding an average group size of 

= 3.0909 with 

variance ( ) = 0.5901.

Table 4—The Boiling Springs, PA, shuttle bus 

tallies on June 2, 2007 

Departure 

time

Shuttle bus people 

count 

Return 

time

number 

9:00 35 9:08 

9:11 20 9:19 

9:20 25 9:27 

9:25 14 9:32 

9:33 21 9:42 

9:41 33 9:49 

9:48 23 9:57 

10:02 48 10:11 

10:10 32 10:20 

10:19 25 10:28 

10:29 42 10:40 

10:38 10 10:46 

10:49 34 11:01 

10:59 33 — 

— 91 a — 

11:50 35 12:03 

12:02 24 12:13 

12:12 20 12:23 

12:20 8 12:29 

12:28 3 12:39 

12:35 4 12:44 

12:50 11 1:01 

 1:03 25 1:14 

 1:10 20 1:20 

 1:21 4 1:30 

 1:25 8 1:34 

 1:36 8 1:46 

 1:40 5 1:48 

 1:51 10 2:00 

 2:08 7 2:19 

 2:14 5 2:24 

 2:25 1 2:33 

 2:32 2 2:38 

 2:40 1 2:47 

 2:48 0 2:58 

 2:53 2 3:03 

 3:04 5 3:13 

 3:14 1 3:22 

 3:23 0 3:34 

 3:28 6 3:52 

 4:01 0 4:10 

— = no observations taken. 

a

A break was taken between 10:59 and 11:50 so no observations 

were recorded for the shuttle buses leaving between this interval.

The value here is an approximation which is derived in the text. 
29

The above estimates could be used to obtain an estimate for . 

Using the general Lincoln-Petersen estimator [equation (40)]

with estimated variance [equation (41)]

and substituting values into equation (38) yields the special 

event estimate

 = 0.5455(1798)(3.0909) = 3,032

with estimated variance [equation (39)] .

Databases and Computer Programs

There are several types of data files created or collected 

in the pilot survey that have been archived as Microsoft 

Excel® files (table 5). These consist of prework spreadsheet 

files and the sample calendar and sample backup file 

created from them. In addition, the observed data collected 

during the sample days are in the day summary and 

individual interview files. The augmented site data from the 

NPS are in two other files. Each of these will now be briefly 

discussed.

The initial step in the pilot survey was to create the 

sampling frame from which the sample was eventually 

selected. To accomplish this, all exiting sites in the 

pilot region had to be identified. In addition, to perform 

an extrapolation to the entire AT, all sites had to be 

identified on the entire AT. This consisted of six prework 

spreadsheet files. The procedure for data entry follows 

that explained previously in the prework dataset section. 

The variable names, type, length, description, and 

permissible values are shown in table 6. The sample 

calendar and sample backup days were generated via a 

SAS program (SAS Institute Inc. 2004) that randomly 

selected the sample days according to specified criteria 

(table 5). 

Table 5—Data files and SAS programs used in the pilot survey and trailwide extrapolation to the entire AT 

File name Description Recordsa

number 

PilotRegion_10152008_SZ.xls Prework 409 

ATCHRegion_10282008_SZ.xls Prework 11

NewEnglandRegion_10142008_LLSZ.xls Prework 631 

MidAtlanticRegion_10202008_LLSZ.xls Prework 770 

Virginia_10142008_LLSZ.xls Prework 467 

SouthernRegion_10142008_LLSZ.xls Prework 348 

calendar.xls Sample calendar 141 

backup.xls Sample backup sample days 184 

ATCH_calendar.xls ATC sample calendar 6 

DSF_A_082008.xls Original day summary data 133 

DSF_B_082108_SZMB.xls Slightly edited day summary data 130

DSF_C_100908_SZMB.xls Final day summary data 130 

IND_A_082008.xls Original individual interview data 1,432 

IND_B_082108_SZMB.xls Slightly edited individual interview data 1,414 

IND_C_090308_SZMB.xls Final individual interview data 1,233 

ATCPROXY_101508_SZ.xls ATC augmented visit data 365 

HFPROXY_10092008_SZ.xls Harpers Ferry augmented visit data 12 

Prework_04252007.sas SAS program to generate the sampling calendar 398 

Prework_ATC.sas SAS program to generate the sampling calendar for 

the ATC 

 46

estimation_02252009.sas SAS program to produce the estimates 3,310 

 .ycnavresnoC liarT naihcalappA = CTA ;liarT cinecS lanoitaN naihcalappA = TAa Does not include the header record if the file is a Microsoft Excel®

 (.xls) data file. 
30

site data are in two files, one for the site-type ATCH 

(ATCPROXY_101508_SZ.xls) and the other for the sitetype HF (HFPROXY_10092008.xls). 

All mathematical and statistical computations were 

performed with SAS-generated programs (SAS Institute 

Inc. 2004). A consistent, structured style was used in the 

programming process, and numerous comments were 

incorporated to aid in explanation of the programming 

steps. The prework programs were developed to read in 

the prework spreadsheets, develop the sampling frame, 

and then select the sample days according to the sample 

design. Two programs performed this function, one for the 

ATC and another for the rest of the pilot region. The major 

programming effort was to develop the SAS estimation 

program which produced the many estimated parameters 

and eventual visitation estimates based on the stratified 

random cluster sampling design. These SAS programs are 

listed in table 5. 

Table 6—The prework data file showing variable names, type, length, description, and 

permissible values 

Variable Type Length Description Valuesa

SITENUM N 8 Site number 0 to 1015

SITETYPE C 3 Site-type ATC, Mb

, P, Sc, TR

USELEVEL C 1 Use-level L, M, H

BEGIN N 8 Beginning date span 101 to 1225

END N 8 Ending date span 101 to 1231

MONDAY N 8 1 = day has this use-level

Blank = does not have this 

use-level 

1, blank

TUESDAY N 8 1 = day has this use-level

Blank = does not have this 

use-level

1, blank

WEDNESDAY N 8 1 = day has this use-level 

Blank = does not have this 

use-level

1, blank 

THURSDAY N 8 1 = day has this use-level 

Blank = does not have this 

use-level

1, blank 

FRIDAY N 8 1 = day has this use-level 

Blank = does not have this 

use-level

1, blank 

SATURDAY N 8 1 = day has this use-level 

Blank = does not have this 

use-level

1, blank 

SUNDAY N 8 1 = day has this use-level 

Blank = does not have this 

use-level

1, blank 

HOLIDAY N 8 1 = day has this use-level 

Blank = does not have this 

use-level 

1, blank 

N = numeric variable; C = character variable; ATC = Appalachian Trail Conservancy; 

TR = trail/road; L = low; M = medium; H = high. a All character values are case sensitive. 

b The site-type MU is coded as M in the data. c The site-type HF is coded as S in the data. 

The observed data consist of standard and augmented site 

data. The day summary files contain basic information 

about the interviewer and the interview process for 

each sample day. Three levels of files are archived. The 

first level is A, which consists of data as entered from 

the field with no edit corrections. This file has limited 

applications but serves as a benchmark for the original 

data. Level B consists of the data after minor, obvious 

errors have been corrected with what are known to be 

true corrections. These data may be useful to certain 

investigators wanting to analyze the data recording 

process itself or perform edit corrections based on their 

own decisions. Level C is a further modification where 

questionable data were altered based on certain logical 

considerations and knowledge about the survey process. 

These are the data that were considered the best for all 

estimates for the pilot survey. Information about the 

variables and their characteristics is listed in table 7. The 

individual interview files are the data recorded for each 

group interviewed for all the sample days. There are 

the A, B, and C versions that serve the same purposes 

as outlined for the day summary files. Table 8 gives 

the characteristics for the variables. The augmented 
31

Table 7—The day summary data file consists of 17 variables and 130 observations (the variables are currently in the 

file in this order based on the questionnaire, although a reordering may be more appropriate for clarity) 

Variable Type Length Description Valuesa

VEHICLESTART N 8 Number of vehicles in parking lot at start of interview period 0 to 89

START N 8 Time at start of interview period (military) 800 to 1630

INTERVIEWER C 14 Person conducting interviews Any name

CLICKPERSON C 14 Person using clicker Any name

DATE N 8 Date of the survey 6/1/2007 to 

8/14/2007 

SITENUM N 8 Site number 0 to 1015

SITENAME C 27 Site name Any name

WEATHER C 19 Weather conditions Any text

BREAK N 8 Break time (minutes) 0 to 90

END N 8 Time at end of interview period (military) 1300 to 2010

SUBSTITUTE C 5 Is this a substitute day?

ORIGINAL C 17 Original SITENUM and day if a substitute day Any text

CLICKER N 8 Total clicker count at end of interview period 0 to 230

TYPE C 8 What was countedb

VEHICLEEND N 8 Number of vehicles in parking lot at end of interview period 0 to 150

SURVEYS N 8 Total number of all surveys completed at end of interview period 0 to 58

NOTES C 502 Notes Any text

N = numeric variable; C = character variable. a All character values are case sensitive. b Vehicles were counted at sites 825, 828, 840, 841, 878, 919, 955, and 999. Site 810, 811, and 813 are blank because there was no 

counting done. Hikers were counted at all other sites. 

NO, YES, EXTRA

HIKERS, VEHICLES,

NOTHING

Pilot Survey Results

Parameter estimates—The calibrating parameters consist 

of the , , and which were estimated with the 

design-based and model-based approaches. A comparison 

of these reveals that the model-based approach produces 

more stable and plausible estimates for the limited amount 

of data available from the pilot survey. The estimated 

and standard errors for all strata for both approaches are 

shown in table 9. The design-based approach yields for 

site-type TR an estimated = 0.500 for use-level L and 

= 1.000 for use-level M. Recalling that is the proportion 

of exiting groups that are recreating and not returning to 

the AT on that day, it seems unreasonable that the true 

parameter values are so incongruent. This is probably due 

to the extremely low sample size of only eight and two 

interviewed groups, respectively. A similar problem occurs 

for stratum HF–L when compared to strata HF–M and HF–

H. Alternately, the model-based approach produces more 

plausible parameter estimates in these situations because it 

incorporates the data from all site-types and use-levels to 

produce much smoother relationships as shown in figure 

6. For all site-types, use-level L is substantially less than 

M and H which are practically identical. In addition, the 

highest is for site-type P followed by TR. This should be 

expected because these site-types are typically used only 

by AT hikers. The ATCH site-type is intermediate due to an 

approximate mixture of AT and non-AT visitors. Site-type 

MU, e.g., State parks through which the AT runs, is a little 

lower, reflecting higher percentages of non-AT visitors. The 

lowest is for site-type HF due to the large proportion 

of visitors that are recreating at Harpers Ferry National 

Historical Park and not using the AT. The standard errors 

are also more reasonable for the model-based approach. 

They are much smoother and are usually less than half that 

of the design-based approach. The estimated and 

reveal similar trends, being smoother and more realistic for 

the model-based approach (tables 10 and 11) (figs. 7 and 8). 

Although the standard errors are usually lower for the modelbased approach, they are not as substantially so as was the 

case for . It is also interesting to note that the model-based 

estimate for is approximately 18 percent larger than that 

of . This supports the need for incorporating both and 

 in the visitation estimators as was given in the “Estimation 

Methodology” section of Part I.

The results for the pilot survey parameter estimates reveal 

several justifications for preferring the model-based 

approach over the design-based approach. First, limited 

available resources resulted in low-sampling intensity for 

certain strata which increased the risk of erratic estimates 

for the design-based approach. This was alleviated to a 

certain extent with the model-based approach because 

all the data are pooled, the relationship between site-type 

and use-level are modeled, and then the individual strata 

estimates are obtained from the model. Second, the modelbased approach smoothes out the parameter estimates so 

that inconsistencies are eliminated to a large degree. For 

instance, if a parameter increases with increasing use-level 

for a given site-type, it will exhibit this pattern for the 

other site-types. The design-based approach does not have 

this property because the individual strata estimates are 
32

Table 8—The individual interview data file consists of 43 variables and 1,233 observations (180 were 

RETURN which were deleted) (the variables are currently in the file in this order based on the questionnaire, 

although a reordering may be more appropriate for clarity) 

Variable Type Length Description Valuesa

INTERVIEWER C 15 Person conducting interviews Any name

MONTH N 8 Month for the survey 6, 7, 8

DAY N 8 Day of the survey 1 to 30

YEAR N 8 Year of the survey 2007

SITENUM N 8 Site number 0 to 1015

SITETYPE C 3 Site-type ATC, Mb

, P, Sc, TR

SITENAME C 27 Site name Any name

AGREE N 8 Person agreed to take survey 

 0 = no 

1 = yes

0, 1 

MATHER N 8 0 = no (only at ATC) 

1 = yes

0, 1 

ATUSE N 8 Person used the AT today 

 0 = no 

1 = yes

0, 1 

REASON C 9 Is AT the primary or secondary

reason for the visit? 

PRIMARY, SECONDARY 

PURPOSE N 8 Purpose of visit

 1 = recreation 

2 = nonrecreation

1, 2

EXIT C 5 Leaving AT for the day LEAVE

TRANS C 7 Transportation mode to AT VEHICLE, BUS, BICYCLE,

WALKING, OTHER

ARRMONTH N 8 Month arrived at AT 2, 3, 4, 5, 6, 7, 8

ARRDAY N 8 Day arrived at AT 1 to 30

ARRYEAR N 8 Year arrived at AT 2007

ARRTIME N 8 Time arrived at AT (military) 500 to 2130

HIKE N 8 Hiking distance on AT today 

 1 = < or = 1 mile 

 2 = over 1 but < 5 miles 

 3 = 5 to < 10 miles 

 4 = 10 or more miles 

1, 2, 3, 4 

VISITS N 8 Visits to this AT site in last 12 monthsd

 0 to 364 

ATVISITS N

N

8

ATVISITS_ADJ Adjusted visits to any AT site in last 12 8

Visits to any AT site in last 12 monthsd 0 to 365

monthsd (corrects original data errors)e 0 to 365 

MALES N 8 Males in group 0 to 22

FEMALES N 8 Females in group 0 to 21

MALES16 N 8 Males < 16 in group 0 to 12

FEMALES16 N 8 Females < 16 in group 0 to 10

NIGHTS N 8 Continuous nights on AT before today 0 to 100

SATISFIED N 8 Satisfaction with AT 

 1 = least satisfied 

10 = most satisfied

5, 6, 7, 8, 9, 10 

CROWDED N 8 Crowding on AT 

 1 = not at all crowded 

9 = extremely crowded

1, 2, 3, 4, 5, 6, 7, 8, 9 

MANAGE C 82 Management Improvements Any text

SPEND N 8 Spent for this AT visit (dollars) 0 to 8000

ZIPCODE N 8 Zip code 1945 to 99999

continued
33

not linked via a common model. Third, the standard errors 

of the parameter estimates are substantially smaller with 

the model-based approach because all the data are pooled 

and used jointly in the estimation process for all strata 

estimates of a parameter. Alternatively, the design-based 

approach estimates a stratum’s parameter based only on 

the data observed in that stratum which results in a smaller 

sample size and, consequently, a larger standard error. 

Despite the advantages of the model-based approach when 

the sampling intensity is low, the design-based approach 

is preferred when adequate sampling is affordable and has 

been achieved. In this situation, the sample-based estimate 

for a given stratum is independent of the other strata and 

is capable of reflecting its individual characteristics and 

properties. It does not rely on a model which assumes no 

interaction between site-type and use-level. This may be 

unrealistic in some surveys.

Guidelines for when to use the two estimation approaches 

are based on professional judgment and somewhat arbitrary 

rules of thumb. Generally, the goal in a survey is to 

estimate a parameter with a coefficient of variation (CV) of 

10 percent or less. The CV is the ratio of the standard error 

divided by the parameter estimate converted to a percent. 

To achieve this for a proportion such as under simple 

random sampling requires a sample size of 100 when 

the estimate of is 0.5. The pilot survey was a cluster 

design so the calculation of required sample size is more 

complicated because sample size is defined by primary 

(clusters) and secondary (total number of observations 

within the clusters) sampling units. However, it is generally 

accepted that clustering is less efficient than simple random 

sampling, so it is safe to assume that the sample size of the 

secondary sampling units should be over 100. Referring 

to table 9, this criterion is not met for most of the strata. 

When parameter estimates are based on means such as 

and , the calculation of required sample size is different, 

but generally a sample size of 30 is considered minimal for 

simple random sampling. Tables 10 and 11 reveal that the 

number of secondary sampling units is usually < 30 which 

is inadequate, even if one discards the cluster nature of the 

sampling design.

Another factor to consider when comparing the designbased and model-based approaches is subject matter 

expertise. Usually an analyst will have some knowledge 

about the parameters that are being estimated and can 

judge which approach produces more desirable estimates. 

For instance, the design-based approach yielded = 0.500

for the TR–L stratum and = 1.000 for the TR–M stratum 

(table 9). It seems highly unlikely that there would be such 

a difference in between the L and M use-levels within 

the site-type TR. The model-based approach yields estimates 

of = 0.586 for the TR–L stratum and = 0.695 for the 

TR–H stratum (table 9) which appear to be more plausible. 

Thus, if this occurs for several of the strata, the modelbased approach is the more desirable approach. However, 

Table 8—The individual interview data file consists of 43 variables and 1,233 observations (180 were RETURN 

which were deleted) (the variables are currently in the file in this order based on the questionnaire, although a 

reordering may be more appropriate for clarity) (continued)

Variable Type Length Description Valuesa

AGE N 8 Age class

 16 = 16 to 20 

 21 = 21 to 30 

 31 = 31 to 40 

 41 = 41 to 50 

 51 = 51 to 60 

 61 = 61 to 70 

71 = 71+

16, 21, 31, 41, 51, 61, 71

GENDER C 1 Gender F, M

HISPANIC N 8 Hispanic or Latino 0, 1

NATIVE N 8 American Indian/Alaska Native 0, 1

ASIAN N 8 Asian 0, 0, 11

BLACK N 8 Black 0,1

PACIFIC N 8 Native Hawaiian/Pacific Islander 0, 1

WHITE N 8 White 0, 1

REFUSED N 8 Refused racial questions 0, 1

CLICKER N 8 Clicker count including this interview 0 to 229

TIME N 8 Time at interview end (military) 802 to 1957

C = character variable; N = numeric variable; ATC = Appalachian Trail Conservancy ; M = multiple use; P = parking; S = 

TR = trail/road; AT = Appalachian National Scenic Trail; F = female; M = male. a All character values are case sensitive. b The site-type MU is coded as M in the data. c The site-type HF is coded as S in the data. d Does not include this visit. e Equals ATVISITS if VISITS is less than or equal to ATVISITS but equals VISITS+ATVISITS if VISITS greater than ATVISITS.

Harpers Ferry;
34

caution must be used here to avoid selecting the approach 

that simply yields parameter estimates that result in any 

preconceived estimate of visitation that the analyst wishes 

to attain from the survey data. 

The average daily clicker count for each strata was 

computed for the standard site-types TR, P, and MU as 

explained previously. They represent the average number 

of people based on a 12-hour day for all groups whether 

they represent LERs or not. The results follow what was 

anticipated with site-type TR being the lowest, site-type 

P being intermediate, and site-type MU being the largest 

(table 12). The use-level relationship was also logical, with 

L being less than M which was less than H. This is not only 

reassuring here but also provides further evidence that the 

prework and stratification process were valid.

The ATCH daily augmented site tallies obtained from 

the ATCH ranged from 10 to 191 during the pilot survey 

period (table 13). Recall that these are the total number of 

people that exited the ATCH during a given day. The daily 

average for the two use-levels was 38.50 for M and 70.59 

for H, which intuitively reflects the prework classification 

and stratification. The conversion from number of people 

to number of groups (LER and non-LER) resulted in 14.78 

for M and 27.31 for H.

The 2007 augmented site data for the site-type HF strata 

were obtained from the official NPS Harpers Ferry 

National Historical Park visitation estimates and reflects 

the sites 810, 811, and 813 (National Park Service 2008). 

The NPS monthly values ranged from 2,447 in February to 

40,522 in July. In order to obtain estimates as outlined in 

the “Estimation Methodology” section of Part I, monthly 

weights had to be obtained for the three use-levels from 

which monthly weighted estimates of , , and were 

computed (table 14). There was little variation for each of 

these estimates over the months. The ranged from 0.074 

to 0.096 with standard errors from 0.0305 to 0.0400. The 

 was even more consistent and ranged from 2.47 to 2.50 

with standard errors from 0.387 to 0.508. The were also 

quite consistent and ranged from 2.81 to 2.85 with standard 

errors ranging from 0.151 to 0.198.

Pilot survey visitation estimates—The visitation 

estimates were calculated based on the previous described 

methodology using the calibrating parameter estimates 

obtained by the design-based and model-based approaches. 

Table 9—The estimated Ph for each site-type and use-level using the 

 

Sitetype Use-level Clusters n 

Designbased

Ph

Designbased

SE

Modelbased

Ph

Modelbased

SE

number

TR L 6 8 0.500 0.256 0.586 0.124

TR M 2 2 1.000 0.000 0.655 0.130

TR H 0 0 1.000a 0.000a 0.695 0.130

 

P L 5 9 0.650 0.138 0.696 0.053

P M 10 40 0.696 0.221 0.765 0.036

P H 18 205 0.819 0.115 0.805 0.025

MU L 4 33 0.273 0.123 0.204 0.049

MU M 13 92 0.273 0.104 0.273 0.031

MU H 20 196 0.300 0.087 0.313 0.025

HF L 2 56 0.018 0.022 0.061 0.049

HF M 4 85 0.165 0.061 0.129 0.030

HF H 10 341 0.164 0.037 0.170 0.020

ATCH L 0 0 0.278b 0.130b 0.355 0.079

ATCH M 2 18 0.278 0.130 0.424 0.067 

ATCH H 4 59 0.508 0.124 0.464 0.063

SE = standard error; TR = trail/road; P = parking; MU = multiple use; HF = Harpers Ferry;

ATCH = Appalachian Trail Conservancy Headquarters; L= low; M = medium;H = high.

a The TR–H stratum had no sample days so the design-based approach Ph

Ph

and SE are 

based on the TR–M stratum.

b The ATCH–L stratum had no sample days so the design-based approach and SE are 

based on the ATCH–M stratum. 

design-based approach and the model-based approach
35

The estimates based on each stratum along with standard 

errors, CVs, and 95-percent confidence intervals are shown 

in table 15. Converting total visits in each stratum to 

visits per day reveals the logical trends for the use-levels. 

Although there were many TR sites, average daily visits 

were slightly < 3 according to either approach. The sitetypes P and MU were similar in visitation over the uselevels, with L being < 10 for both, while H ranged to near 

60. The augmented site ATCH average daily visitation was 

about 17 for M and 30 for H. The augmented site-type HF 

did not allow for individual use-level estimates because 

only monthly augmented data were available.

The pilot survey estimates reveal that the bulk of the 

visitation is from the P and MU site-types. Although there 

are many TR site days, the average visits per day are so 

low that their total visits are only about half or less than 

those of site-types MU or P. Nevertheless, because of the 

large number of site days, the TR–L stratum produces the 

second most visits of any individual stratum (table 15). The 

augmented site-types ATCH and HF have relatively large 

average daily visitation but have few site days which also 

result in low total visitation. 

A comparison of the total visit estimates on a strata basis 

for the two approaches reveals that they are quite similar 

for site-type P, MU, and ATCH for use-level H while for 

the other two use-levels they were substantially different 

with no pattern being exhibited. The estimates for site-type 

TR varied depending on use-level with the model-based 

approach being lower for use-level L while the designbased approach was lower for use-level M. The ATCH 

site-type produced very nearly the same estimates for both 

approaches, but the HF site-type was much different with 

the model-based approach yielding almost three times 

as much visitation as the design-based approach. The 

precision of the estimates which depends on the standard 

error is best viewed through the CV which gives the 

standard error as a percent of the estimates. In nearly all 

strata the CV for the model-based approach is less than 

the design-based approach. Despite this, both approaches 

have CVs that are usually much over 15 percent. This is 

reflected in many of the confidence intervals being very 

wide, with some actually having negative values. Thus, 

strata-level estimates of visitation should be viewed 

with caution because of the large level of variability due 

to small sample size. It should be remembered that the 

objective of this survey was for an overall estimate in the 

pilot area and not strata-level estimates. If strata-level 

estimates are needed for future surveys, the sample sizes 

should be increased accordingly.

The comparison of the design-based and model-based 

approaches indicates that very different estimates may 

often be obtained due to the differences in estimating 

the calibration parameters , , and as described 

previously. In this case, the model-based approach appears 

more consistent with logical relationships for these 

calibration parameters than the design-based approach. 

In addition, it produces smaller estimates of the standard 

errors of the calibration parameters and strata visitation 

estimates. Thus, the pilot survey visitation estimate will be 

based upon the model-based approach. However, in other 

surveys it is recommended that the design-based approach 

be considered, especially when sufficient sample size is 

available to produce more stable estimates. 

The pilot survey was principally designed to obtain overall 

visitation from June 1 through August 14, 2007, on the 

AT from Harpers Ferry, WV, to 10 trail miles north of 

Boiling Springs, PA, at the Scott Farm. Thus, combining 

the model-based estimates over the standard site-types, the 

augmented site-type ATCH, the augmented site-type HF, 

and the special event yields the visitation estimates shown 

in table 16. The total visitation for the pilot survey using 

1.0

0.8

0.6

0.4

0.2

0.0

1.0

0.8

0.6

0.4

0.2

0.0

1 2 3

Use-level

1 2 3

Use-level

(A)

(B)

PBAR PBAR

Figure 6—The relationship of estimated and use-level for the five 

site-types using (A) the design-based approach and (B) the modelbased approach. The circles represent the standard strata where 

TR = solid, P = long dash, and MU = short dash. The stars represent 

the augmented strata where HF = solid and ATCH = long dash.
36

the model-based approach was 70,912 with 95-percent 

confidence intervals of 48,678 to 93,146. The CV was 

16 percent which is considered quite good especially for 

the low level of sampling that was performed. The bulk 

of the visitation (83 percent) could be attributed to the 

standard sites types. The three HF sites at Harpers Ferry 

contributed a moderate share (9 percent), while the ATCH 

had a relatively small contribution (3 percent). However, 

it should be noted that these augmented site-types (HF and 

ATCH) in Harpers Ferry account for about 12 percent of 

all AT visitation for the pilot survey. This is a large share 

considering the mileage of the AT running through Harpers 

Ferry relative to the mileage of the AT included in the pilot 

survey. 

Part II—Trailwide Extrapolation (TWE)

Overview

The estimates from the pilot survey were based on data 

collected over the spatial and temporal inference spaces 

defined by the objectives of the survey; however, resource 

limitations precluded sampling over the entire AT for the 

whole year. Thus, for the TWE, some caution must be 

used when interpreting the various estimates and when 

using these estimates for management purposes. The first 

major assumption that was imposed is that the calibrating 

parameters , , and for the TWE are the same as for 

the pilot survey. The stratification process of classifying site 

days into site-types and use-levels should theoretically help 

to satisfy this assumption to a certain degree. For example, if 

a site was in stratum MU–L during the pilot survey, its group 

size is probably quite similar to another site in stratum 

MU–L during the winter. However, it must be emphasized 

that the spring, fall, and winter did not contribute any standard 

site data to the estimates and, thus, it is inevitable that some 

differences could exist temporally and spatially. A second 

major assumption that may be more critical and difficult 

to accept is that the exit tallies are the same for the pilot 

survey and the TWE. Although this issue was carefully 

considered and incorporated into the stratification process 

used for the whole AT, the pilot survey strata sample means 

could potentially be biased upwards with respect to the TWE 

because they are based only on summer data when there 

Table 10—The estimated Gh for each site-type and use-level using the designbased approach and the model-based approach 

Sitetype Use-level Clusters n 

Designbased

Gh

Designbased

SE 

Modelbased

Gh

Modelbased

SE 

number

TR L 4 4 3.000 2.126 2.377 0.893

TR M 2 2 1.000 0.000 2.246 0.960

TR H 0 0 1.000a 0.000a 2.385 0.963

P L 4 6 2.375 0.861 2.699 0.579

P M 10 25 2.748 0.910 2.567 0.297

P H 18 174 2.690 0.150 2.706 0.159

MU L 3 9 2.600 0.421 2.602 0.570

MU M 9 25 2.109 0.246 2.470 0.309

MU H 12 59 2.771 0.370 2.609 0.250

HF L 1 1 1.000 0.000b 2.506 0.623

HF M 4 14 2.571 0.823 2.374 0.346

HF H 10 63 2.478 0.332 2.514 0.260

ATCH L 0 0 4.000c 0.800c 2.441 0.767

ATCH M 2 5 4.000 0.800 2.309 0.568

ATCH H 4 30 2.167 0.343 2.449 0.511

SE = standard error; TR = trail/road; P = parking; MU = multiple use; HF = Harpers Ferry; 

ATCH = Appalachian Trail Conservancy Headquarters; L= low; M = medium; H = high.

a The TR–H stratum had no sample days so the design-based approach Gh and SE are based on 

the TR–M stratum. 

b The HF–L stratum had only one observation so the design-based approach SE was set to 0.000

for computational simplicity. 

c The ATCH–L stratum had no sample days so the design-based approach Gh and SE are based 

on the ATCH–M stratum. 
37

is more opportunity for larger groups with children to use 

the AT. A final major assumption for the TWE is that there 

were no festivals or events analogous to the special event at 

Boiling Springs where AT usage would have exceeded the 

L, M, and H exit volume levels for the various site-types. 

Omitting such days or events could lead to a negative bias in 

the extrapolation results. Despite these problems, the TWE 

estimation process described below is the optimal approach in 

lieu of the resources necessary to sample along the entire AT 

during the course of a complete year.

Sampling Design

The first step in the TWE was the prework which developed 

the sampling frame consisting of all site days along the 

entire AT from Mount Katahdin, ME, to Springer Mountain, 

GA, from January 1, 2007, to December 31, 2007. This was 

performed as was described for the pilot survey and included 

the New England, mid-Atlantic, Virginia, and southern 

regions. Stratification was formed by the classification 

of all site days into the 15 potential strata formed by the 

combination of the 5 site-types and 3 use-levels. Unlike 

the pilot survey, the TWE did contain site days in strata 

ATCH–L and TR–H in which case special modifications 

were employed to obtain the intermediate quantities needed 

for visitation estimation. Due to limited resources and time, 

no other sites were added to the site-type HF strata except 

those previously discussed at Harpers Ferry, WV, which 

were expanded to include the entire year. This was also the 

case for site-type ATCH. Similarly, no special events other 

than Foundry Day at Boiling Springs, PA, on June 2 were 

identified for the TWE. Undoubtedly there may be other 

Group size

4

3

2

1

0

4

3

2

1

0

Group size

1 2 3

Use-level

1 2 3

Use-level

(A)

(B)

Figure 7—The relationship of estimated and use-level for the 

five site-types using (A) the design-based approach and (B) the 

model-based approach. The circles represent the standard strata 

where TR = solid, P = long dash, and MU = short dash. The stars 

represent the augmented strata where HF = solid and ATCH = long 

dash.

5

4

3

2

1

0

All group size

5

4

3

2

1

0

All group size

1 2 3

Use-level

1 2 3

Use-level

(A)

(B)

Figure 8—The relationship of estimated and use-level for the five 

site-types using (A) the design-based approach and (B) the modelbased approach. The circles represent the standard strata where 

TR = solid, P = long dash, and MU = short dash. The stars represent 

the augmented strata where HF = solid and ATCH = long dash.
38

site days along the AT with extraordinary characteristics 

like the site-types HF and ATCH, and special event at 

Boiling Springs. If such site days exist and are not explicitly 

accounted for, the TWE will exhibit a negative bias and be 

conservative. Future recommendations suggest that efforts 

be used to identify such sites along the entire AT. 

The total TWE sampling frame consisted of 332,434 

site days excluding the special event distributed by 

site-type and use-level as shown in table 2. The TR–L 

stratum had the most site days, totaling 56 percent of the 

entire sampling frame followed by P–L with 24 percent. 

Although these two strata may represent low levels of 

daily visitation, they comprise 80 percent of all site days 

and, therefore, may have a large impact on the visitation 

estimate. The TWE designated all TR, P, and MU as 

standard site-types and the HF and ATCH as augmented 

site-types.

The number of sites identified as unique exit points for 

each of the regions was New England = 239, mid-Atlantic 

(excluding pilot) = 319, pilot = 120, Virginia = 146, and 

southern = 129, for a total of 953 with 849 open during the 

entire year. The percent of sites open all year for each of 

the regions was New England = 67 percent, mid-Atlantic 

(excluding pilot) = 98 percent, pilot = 99 percent, 

Table 12—The average clicker count per sample day for 

each stratum adjusted to a 12-hour recreation day (this 

represents the average number of groups of all types of 

people exiting) 

Sitetype Use-level Sample 

days Average SE 

number 

 

TR L 12 1.880 0.761 

TR M 9 0.506 0.375 

TR H 0 0.506a 0.375a

 

P L 11 2.518 1.535 

P M 13 6.750 2.144 

P H 20 26.704 4.622 

 

MU L 7 13.689 9.603 

MU M 15 31.199 6.966 

MU H 21 51.939 17.436 

SE = standard error; TR = trail/road; P = parking; MU = multiple use; 

L= low; M = medium; H = high. 

a

 The TR–H stratum had no sample days so the average and SE are 

based on the TR–M stratum. 

Table 11—The estimated a Gh for each site-type and use-level using the 

design-based approach and the model-based approach 

Sitetype Use-level Clusters n

Designbased

a Gh

Designbased

SE 

Modelbased

a Gh

Modelbased

SE 

number

TR L 6 8 4.500 1.944 3.838 0.631

TR M 2 2 1.000 0.000 3.649 0.662

TR H 0 0 1.000a 0.000a 3.630 0.661

 

P L 5 9 1.800 0.508 2.817 0.263

P M 10 40 2.561 0.649 2.629 0.177

P H 18 204 2.664 0.110 2.610 0.129

MU L 5 41 2.896 0.452 2.943 0.236

MU M 13 101 2.542 0.216 2.755 0.149

MU H 19 189 2.871 0.249 2.736 0.128

HF L 2 54 3.074 0.348 2.887 0.242

HF M 4 110 2.973 0.266 2.698 0.143

HF H 10 384 2.584 0.105 2.679 0.096

ATCH L 0 0 2.474b 0.061b 2.792 0.398

ATCH M 2 19 2.474 0.061 2.604 0.337

ATCH H 4 59 2.627 0.545 2.585 0.321

SE = standard error; TR = trail/road; P = parking; MU = multiple use; HF = Harpers 

Ferry; ATCH = Appalachian Trail Conservancy Headquarters; L= low; M = medium; H = high.

a The TR–H stratum had no sample days so the design-based approach a Gh and SE are based

on the TR–M stratum. 

b The ATCH–L stratum had no sample days so the design-based approach a Gh and SE are based 

on the ATCH–M stratum. 
39

 Virginia = 100 percent, and southern = 86 percent, with 

the overall being 89 percent. The prework spreadsheet 

for the site-type ATCH was based on the augmented site 

data obtained from the ATCH Office in Harpers Ferry, 

WV, for the entire year as explained previously. The sitetype HF was increased to include the NPS Harpers Ferry 

National Historical Park monthly visitation estimates for 

the entire year. The TWE did not consist of any additional 

sampling but utilized the same sample selection and survey 

procedures used by the pilot survey.

Estimation Methodology

The TWE used the design-based approach and the modelbased approach for estimation of the calibrating parameters. 

The model-based approach was particularly appealing 

because it allowed for an estimation of the ATCH–L and 

TR–H strata parameters which were needed for the TWE 

visitation estimates despite no data for these strata being 

collected during the pilot survey. Relevant parameter 

estimates were derived using the relationships among all the 

site-types and use-levels developed with pilot survey data. 

However, the design-based approach used a somewhat more 

arbitrary method to obtain these missing values by merely 

substituting the parameter estimate from the closest use-level 

in the site-type. 

Total visitation for the TWE for the entire 2007 year is 

defined by equation (13) except that VISITS is the total 

number of recreation visits on the entire AT from January 1 

to December 31, 2007.

The standard site-type component which consists of sites in 

the strata composed of the TR, P, and MU site-types and all 

three use-levels L, M, and H is obtained by equation (15) 

where the summation is extended from h = 1 to 9 due to 

the inclusion of stratum TR–H. The TWE uses the Nh based 

on the total AT prework data (table 2), but the , , and 

 are obtained from the pilot survey based on equations 

(17), (19), and (22), respectively.

The augmented site-type ATCH data consisted of the 

328 daily visitor tallies that the ATCH Office in Harpers 

Ferry, WV, obtained throughout the entire year (only pilot 

survey data is shown in table 13). Note that 37 days were 

missed due to official closure of the ATCH or due to poor 

weather conditions (table 17). This was combined with the 

estimates and obtained from the 6 sample site days 

taken during the pilot survey at the ATCH.

Let

Nh

 = total number of days that the ATCH has days in 

 use-level (h = L M H) during the entire year 

nh = number of days the ATCH tallied visitation for 

 stratum h during the entire year

 = the ATCH visitation tally on day i in use-level h

then, the average daily augmented site-type visitation tally 

in use-level h is the arithmetic mean as defined in equation 

(24). However, the estimated variance in equation (25) does 

not equal zero because nh

 is less than Nh for use-level L and 

M, resulting in a nonvanishing finite population correction. 

The estimate for the ATCH for the TWE is obtained from 

equation (26) by extending the summation over all three 

use-levels and , , and are calculated from the pilot 

survey data using equations (17), (22), and (27), respectively. 

As mentioned for the pilot survey, the variance equation (26) 

is quite complicated because it is a product of a constant and 

three variables as well as a ratio of a dependent variable. 

Previously, it was assumed that was a constant, which 

is reasonable because its variance is quite small and it is 

highly correlated with . However, due to the nonvanishing 

finite population correction ≠0 for the TWE, a 

simplification cannot be made. Therefore, equation (29) is 

extended over all three use-levels and modified as

Table 13—Augmented counts for the ATCH from 9:00 a.m. 

until 4:00 or 5:00 p.m. for the pilot survey from June 1 to 

August 14, 2007 

Date Visitors Hours Date Visitors Hours

 - - - number - - - - - - number - - - 

06/01/07 58 8 07/09/07 44 8

06/02/07 176 7 07/10/07 62 8

06/03/07 80 7 07/11/07 43 8

06/04/07 61 8 07/12/07 64 8

06/05/07 51 8 07/13/07 121 8

06/06/07 67 8 07/14/07 78 7

06/07/07 41 8 07/15/07 46 7

06/08/07 60 8 07/16/07 65 8

06/09/07 93 7 07/17/07 48 8

06/10/07 85 7 07/18/07 32 8

06/11/07 50 8 07/19/07 30 8

06/12/07 66 8 07/20/07 39 8

06/13/07 39 8 07/21/07 127 7

06/14/07 71 8 07/22/07 52 7

06/15/07 101 8 07/23/07 52 8

06/16/07 122 7 07/24/07 52 8

06/17/07 77 7 07/25/07 20 8

06/18/07 68 8 07/26/07 47 8

06/19/07 75 8 07/27/07 31 8

06/20/07 37 8 07/28/07 80 7

06/21/07 65 8 07/29/07 43 7

06/22/07 76 8 07/30/07 65 8

06/23/07 191 7 07/31/07 25 8

06/24/07 63 7 08/01/07 47 8

06/25/07 61 8 08/02/07 35 8

06/26/07 58 8 08/03/07 31 8

06/27/07 72 8 08/04/07 55 7

06/28/07 78 8 08/05/07 48 7

06/29/07 78 8 08/06/07 10 8

06/30/07 109 7 08/07/07 45 8

07/01/07 148 7 08/08/07 33 8

07/02/07 102 8 08/09/07 24 8

07/03/07 62 8 08/10/07 26 8

07/04/07 88 7 08/11/07 84 7

07/05/07 54 8 08/12/07 42 7

07/06/07 80 8 08/13/07 38 8

07/07/07 109 7 08/14/07 21 8

07/08/07 68 7

ATCH = Appalachian Trail Conservancy Headquarters. 
40

=

=

 

(43)

The site-type HF sites consisted of the three sites located 

at Harpers Ferry (810, 811, and 813) and were estimated 

using the official monthly NPS Harpers Ferry National 

Historic Site visitation estimates as augmented site data 

as was done for the pilot survey (table 14). This provided 

visitation estimates based on data for the total 365 days at 

Harpers Ferry which was considered superior to visitation 

estimates derived from the 20 site days that were planned 

to be sampled during the pilot study. However, there were 

several limitations to using this augmented site data that had 

to be resolved. Recall that the NPS visitation included both 

AT and non-AT visits and was not stratified by use-level and 

was on a monthly basis. To resolve these problems required 

a monthly derived from weighting the individual three 

use-level estimates obtained from the pilot study for site-type 

HF by the monthly strata weights obtained from the prework 

spreadsheet data as shown in equation (30). To convert the 

NPS people tally to group tally a similar weighted mean 

of all group size was computed with equation (32). Also 

required was the monthly average group size for AT LERs 

defined by equation (34). The visitation for the TWE utilizes 

these monthly weighted estimates and the monthly NPS 

augmented site-type visitation estimate and is defined by 

modifying equation (36) to extend over all 12 months with

k = 1 for all months.

The only special event identified for the TWE was Foundry 

Day at Boiling Springs, PA, on June 2, 2007. Thus, the 

estimate from the pilot was simply used in this instance.

Extrapolation Results

The visitation estimates were calculated based on the 

previously described methodology using the calibrating 

parameter estimates obtained by the pilot survey. 

Estimates were based on the design-based and modelbased approaches for comparison purposes. The estimates 

based on each stratum along with standard errors, CV, and 

95-percent confidence intervals are shown in table 18. The 

TWE is based on data from the pilot survey and, thus, the 

relationships discussed previously are generally the same 

here.

The TWE estimates for both approaches are shown in table 

16 for the standard site-types, the augmented site-type 

ATCH, the augmented site-type HF, the special event, and 

the total. The total visitation for the entire AT using the 

model-based approach was 1,948,701 with a 95-percent 

confidence interval of 1,172,146 to 2,725,256. 

Table 14—The monthly augmented counts, strata weights, weighted Pi , Gi , and a Gi

 estimates, and 

standard errors for the Harpers Ferry augmented data under the model-based approach 

Month 

Monthly 

 augmented count 

Strata weights _ 

 L M H Pi

Pi

SE Gi

Gi

SE a Gi

a Gi

SE 

number 

 

Jan. 3,389 74 17 2 0.076 0.0393 2.48 0.500 2.85 0.194 

Feb. 2,447 68 16 0 0.074 0.0400 2.48 0.508 2.85 0.198 

Mar. 10,803 75 18 0 0.074 0.0399 2.48 0.507 2.85 0.197 

Apr. 20,390 63 9 18 0.089 0.0346 2.49 0.440 2.83 0.171 

May 32,597 66 9 18 0.088 0.0350 2.49 0.446 2.83 0.173 

June 32,243 63 9 18 0.089 0.0346 2.49 0.440 2.83 0.171 

July 40,522 63 10 20 0.091 0.0336 2.49 0.427 2.82 0.166 

Aug. 26,520 69 8 16 0.085 0.0365 2.50 0.465 2.83 0.181 

Sept. 28,160 57 11 22 0.096 0.0316 2.49 0.402 2.81 0.156 

Oct. 32,243 66 9 18 0.088 0.0350 2.49 0.446 2.83 0.173 

Nov. 15,383 71 17 2 0.076 0.0390 2.48 0.496 2.85 0.193 

Dec. 5,211 56 23 14 0.094 0.0305 2.47 0.387 2.81 0.151 

 Total 249,908 

L = low; M = medium; H = high; SE = standard error. 
41

 The CV was 20 percent which is considered quite 

good especially for the low level of sampling that was 

performed. The bulk of the visitation (99 percent) could 

be attributed to the standard sites because any additional 

sites like the site-types HF and ATCH and the special event 

were not identified outside of the pilot survey area.

The TWE using the design-based approach yields similar 

findings to the model-based approach. The overall 

visitation estimate with the design-based approach is 

1,925,044 with a 95-percent confidence interval of 

886,457 to 2,963,630, and a CV of 28 percent.

Table 15—Pilot survey visitation (site-type HF represents the summation over all use-levels and 

all three sites because monthly augmented data were used) 

 

Site- Uselevel 

Total 

site 

days 

Visits 

per day 

Total 

visits

Standard 

error

Coefficient 

of 

variation 

Lower 

95 

CI

Upper 

95 

CI

- - - - - - - - - number - - - - - - - - - - percent 

 

TR L 3,624 2.8 10,217 8,505 83 −6,453 26,887 

TR L 3,624 2.6 9,493 5,318 56 −931 19,918 

 

TR M 651 0.5 329 244 74 −150 808 

TR M 651 0.7 484 390 80 −279 1,248 

 

TR H 0 — — — — — — 

TR H 0 — — — — — — 

 

P L 1,781 3.9 6,923 4,792 69 −2,469 16,315 

P L 1,781 4.7 8,422 5,355 64 −2,073 18,917 

 

P M 689 12.9 8,893 4,710 53 −339 18,125 

P M 689 13.2 9,127 3,094 34 3,063 15,191 

 

P H 80 58.8 4,704 1,072 23 2,603 6,806 

P H 80 58.2 4,653 861 19 2,965 6,341 

 

MU L 1,161 9.7 11,269 8,778 78 −5,936 28,475 

MU L 1,161 7.3 8,430 6,217 74 −3,756 20,616 

 

MU M 542 18.0 9,732 4,331 45 1,243 18,221 

MU M 542 21.0 11,382 3,148 28 5,213 17,551 

 

MU H 167 43.1 7,205 3,241 45 852 13,557 

MU H 167 42.4 7,078 2,518 36 2,144 12,012 

 

ATCH L 0 — — — — — — 

ATCH L 0 — — — — — — 

 

ATCH M 14 17.3 242 121 50 5 479 

ATCH M 14 14.5 203 59 29 87 318 

 

ATCH H 61 29.6 1,806 521 29 785 2,827 

ATCH H 61 31.0 1,892 469 25 973 2,811 

 

HF L, M, H 75 34.8 2,614 499 19 1,636 3,591 

HF L, M, H 75 89.5 6,716 1,740 26 3,306 10,125 

 

Special — — — 3,032 1,765 58 −427 6,491 

 

 Total design-based estimates 66,967 15,122 23 37,328 96,605 

 Total model-based estimates 70,912 11,344 16 48,678 93,146 

Note: 

— = no data; CI = confidence intervals; TR = trail/road; P = parking; MU = multiple use; ATCH = Appalachian 

Trail Conservancy Headquarters; HF = Harpers Ferry; L= low; M = medium; H = high. 

The first line of each pair represents the design-based estimates and the second the model-based estimates.

type
42

Table 16—The final visitation estimates for the pilot survey and the trailwide extrapolation 

for the entire AT 

 

Estimate 

Total 

visits 

Standard 

error 

Coefficient of 

variation 

Lower 95 

CI 

Upper 95 

CI 

number 

Design-based approach 

Pilot Standard 59,273 15,001 25 29,872 88,674 

Pilot ATCH 2,048 535 26 1,000 3,096 

Pilot HF 2,614 499 19 1,636 3,591 

Pilot SE 3,032 1,765 58 −427 6,491 

Pilot total 66,967 15,122 23 37,328 96,605 

Model-based approach 

Pilot Standard 59,070 11,060 19 37,392 80,747 

Pilot ATCH 2,095 472 23 1,169 3,021 

Pilot HF 6,716 1,740 26 3,306 10,125 

3,032 1,765 58 −427 6,491 

70,912 11,344 16 48,678 93,146 

AT Standard 1,908,847 529,885 28 870,272 2,947,423 

AT ATCH 5,720 1,468 26 2,844 8,597 

AT HF 7,444 788 11 5,899 8,989 

3,032 1,765 58 −427 6,491 

1,925,044 529,891 28 886,457 2,963,630 

Model-based approach 

AT Standard 1,921,047 396,187 21 1,144,522 2,697,573 

AT ATCH 5,239 916 17 3,444 7,034 

AT HF 19,383 2,785 14 13,923 24,842 

 3,032 1,765 58 −427 6,491 

1,948,701 396,201 20 1,172,146 2,725,256

AT = Appalachian National Scenic Trail; CI = confidence intervals; ATCH = Appalachian Trail Conservancy

 Headquarters; HF = Harpers Ferry; SE = special event. 

Pilot SE

Pilot total

AT SE

AT total

AT SE

AT total

Design-based approach 

Table 17—The days when the ATCH Office in 

Harpers Ferry, WV, was officially closed or closed 

due to weather (some closed days had visitor 

counts because they were opened partially or 

closed early due to bad weather conditions) 

Month Officially closed 

 (date)

Due to weather 

 (date) 

January 1, 6, 7, 13, 14, 15, 

20, 21, 27, 28 

 18 

February 3, 4, 10, 11, 17, 18, 

19, 24, 25 

 8, 13, 14 

March 3, 4, 10, 11, 17, 18, 

24, 25 

November 22 

December 22, 23, 25, 29, 30 

ATCH = Appalachian Trail Conservancy Headquarters.
43

Part III—Conclusions and 

Limitations

The main objective of this research was to develop a 

prototype survey design that could be used for estimating 

visitation on long, linear trails and apply this prototype to 

a major portion of the AT. The survey design framework 

produced a sampling frame based on exit sites that can 

be stratified by site-type and expected use-level or exit 

volume. It is believed that this structure could easily and 

efficiently be applied to other segments of the AT, as well 

as other long trails, with only minor modifications such as 

additional site-types and/or use-levels for both standard 

and augmented sites, and special events. The results of the 

pilot survey, using the model-based approach, yielded a 

visitation estimate of 70,912, with a 95-percent confidence 

interval of 48,678 to 93,146, for the 75-day time period in 

2007 from Harpers Ferry to 10 trail miles north of Boiling 

Springs, PA, at the Scott Farm. 

Satisfying a second major research objective, these 

model-based results were extrapolated to produce an 

annual 2007 visitation estimate for entire AT of 1,948,701 

with a 95-percent confidence interval of 1,172,146 to 

2,725,256. This estimate is about 50 percent less than the 

previously reported annual AT visitation of 3 to 4 million 

(Appalachian Trail Conservancy 2009, National Park 

Service 2009a). Although the annual visitation estimate 

for the entire trail produced by our methodology is an 

extrapolation from the pilot survey, and is, thus, dependent 

on a number of assumptions (see the “Overview” 

section, pages 36-37), it is scientifically defensible, and 

the methodology provides a structure for examining the 

various assumptions through sensitivity analyses.

The third objective of this project was to provide a 

preliminary estimate of the resources required for a survey 

of the entire Appalachian Trail for a full year as opposed 

to an extrapolation based on the pilot survey. Although it 

is possible to determine the number of sample site days 

required to achieve a specified level of precision given the 

total number of site days and level of variability for each 

stratum, we are only providing a rough guideline here. This 

is because the variances were at times poorly estimated, 

especially for the TR site-type where the use-levels were 

based on low-sample size or for TR–H, not estimated at all.

First, consider that 25 sample site days are needed to 

provide an estimate of the strata means for each of the 3 

use-levels in each of the site-types TR, P, and MU that are 

remotely located along the AT. Generally, a sample size of 

25 is considered appropriate for a sample mean because 

this is where the t-distribution closely approaches the 

normal distribution and asymptotic properties of estimators 

begin to be achieved. Theoretically, a stratum like TR–L 

that has more total site days and possibly greater variability 

should have greater allocation than a stratum like MU–H. 

However, the visitation in TR–L is very low, and it is 

felt more important to allocate more resources where 

the visitation is higher as in MU–H which will provide 

more interviews that are not only useful for the visitation 

estimate but also for any of the other estimates that are 

addressed in the survey questionnaire. It is important to 

also keep in mind that at these sites where daily visitation 

may be low, especially site-type TR, some of the 25 site 

days may have no visitors and, hence, contribute no data 

for estimating some of the visitation parameters. Thus, 

allocating an equal sample size of 25 site days appears to 

be a good compromise between theoretical and practical 

considerations. The other two site-types, ATCH and HF, 

are both located in Harpers Ferry, WV, and consist of only 

one and three sites, respectively. Thus, it was felt that 30 

site days for each of these site-types, 10 per use-level, 

would be adequate. There was one special event in the 

pilot study, but the total number along the entire AT was 

unknown. Thus, for lack of information, we assume there 

is one additional special event per each of the four AT 

regions, yielding five special events in total. Based on 

this allocation, it is estimated that 290 sample site days 

distributed throughout the year would be adequate for a 

total annual AT visitation estimate.

The cost associated with sampling 290 site days and 

the analysis of the data consists of several components. 

Assuming an 8-hour survey day at $15 per hour and 

transportation costs of $20, gives a total cost of $140 per 

day or $40,600 for all 290 site days. The data entry costs 

consist of manually entering data from the daily summary 

forms and the interview forms for each site day at a rate of 

$15 per hour. The cost of entering all the daily summary 

forms is $435 assuming an entry rate of 10 per hour. 

Assuming 20 interviews per site day, the interview forms, 

which are a little longer and can be entered 8 per hour, 

would cost $10,875. Additional effort is needed for data 

editing, adjustments to the estimation computer program, 

analysis, and report writing, totaling $30,000. Fortunately, 

the questionnaire development and stratification of the 

entire AT has already been accomplished and will entail 

no further costs. Travel, logistics, supplies, postage, and 

other miscellaneous items total an additional $5,000. Thus, 

an approximate estimate for performing an entire annual 

AT visitation survey would be $86,910. There is potential 

to reduce this by a substantial amount by not having to 

pay interviewers for their labor and data entry if sufficient 

volunteers could be obtained. With surveying spread over 

the entire year and trail, the concentration of interviewer 

work would also be spread out and this would probably be 

more conducive to obtaining volunteers.

The distinction between standard and augmented sites 

proved quite useful for separating groups of estimators and 

resulted into more efficient estimators. Augmented sites 

are advantageous because they contain a “known” quantity 

that can be exploited to produce a less variable visitation 
44

Table 18—Trailwide extrapolation visitation (site-type HF represents the summation over all uselevels and all three sites because monthly augmented data were used)

Sitetype Uselevel 

Total 

site 

days 

Visits 

per 

day 

Total 

visits 

Standard 

error 

Coefficient 

of variation 

Lower 

 95 

CI 

Upper 

95 

CI 

- - - - - - - - - - number - - - - - - - - - 

TR L 184,988 2.8 521,552 434,145 83 −329,372 1,372,476 

TR L 184,988 2.6 484,593 271,482 56 −47,512 1,016,699 

 

TR M 8,112 0.5 4,103 3,044 74 −1,864 10,069 

TR M 8,112 0.7 6,033 4,854 80 −3,480 15,547 

 

TR H 9,490 0.5 4,800 3,561 74 −2,181 11,780 

TR H 9,490 0.8 7,957 6,351 80 −4,490 20,404 

 

P L 81,429 3.9 316,510 219,085 69 −112,896 745,916 

P L 81,429 4.7 385,048 244,821 64 −94,801 864,898 

 

P M 19,140 12.9 247,039 130,846 53 −9,420 503,497 

P M 19,140 13.2 253,553 85,944 34 85,102 422,004 

 

P H 8,625 58.8 507,200 115,581 23 280,661 733,739 

P H 8,625 58.2 501,664 92,837 19 319,704 683,625 

 

MU L 13,279 9.7 128,893 100,403 78 −67,898 325,684 

MU L 13,279 7.3 96,417 71,110 74 −42,959 235,792 

 

MU M 3,028 18.0 54,372 24,197 45 6,946 101,797 

MU M 3,028 21.0 63,589 17,585 28 29,123 98,055 

 

MU H 2,883 43.1 124,380 55,953 45 14,712 234,049 

MU H 2,883 42.4 122,193 43,462 36 37,008 207,377 

 

ATCH L 120 5.6 676 338 50 15 1,338 

ATCH L 120 3.9 467 177 38 120 815 

 

ATCH M 157 15.5 2,431 1,213 50 53 4,808 

ATCH M 157 13.0 2,033 589 29 837 3,188 

 

ATCH H 88 29.7 2,613 754 29 1,136 4,091 

ATCH H 88 31.1 2,739 678 25 1,409 4,046 

 

HF L, M, H 365 20.4 7,444 788 11 5,899 8,989 

HF L, M, H 365 53.1 19,383 2,785 14 13,923 24,842 

 

Special — — — 3,032 1,765 58 −427 6,491 

 

 Total design-based estimates 1,925,044 529,891 28 886,457 2,963,630 

 Total model-based estimates 1,948,701 396,201 20 1,172,146 2,725,256 

— = Entries do not apply to the Special site-type. 

TNote: he first line of each pair represents the design -based estimates and the second the model-based estimates.

 HF = Harpers Ferry; TR = trail/road; P = parking; MU = multiple use; 

ATCH = Appalachian Trail Conservancy Headquarters; L = low; M = medium; H = high.
45

estimate based in part on data that is collected outside the 

survey. In addition, this can lead to more optimal use of 

limited resources. In the present study, there were only 

two augmented site-types, HF and ATCH, but in other trail 

surveys there may be numerous ones depending on the 

level of auxiliary information that is known about the trail. 

The HF augmented site-type illustrated use of auxiliary 

data consisting of NPS monthly visitation estimates, while 

the ATCH augmented site-type was based on very accurate 

daily visitation tallies obtained from the ATC. These 

illustrated two different methodologies to convert these 

augmented site-types to appropriate visitation estimates. 

Undoubtedly, other sections of the AT, or other trails in 

general, could have different augmented site-types such as 

fee tickets, parking lot counts, or mandatory registration 

that would require further adaptation of these methods for 

conversion. 

There was only one special event identified in the survey 

and the application of mark-recapture methods commonly 

used with wildlife population was found useful in 

estimating this visitation. The value of isolating a special 

event instead of simply including the 3 site days in the 

MU-L stratum and the 2 site days in the MU–H stratum 

resulted in 3,032 visits instead of 3(7.3)+2(42.4)=106.7 

visits obtained using the relevant standard site-type 

information. This difference emphasizes the importance of 

identifying all special events in future surveys. Obviously, 

special events require knowledge of the site(s), and other 

innovative techniques besides mark-recapture methods may 

have to be employed. It is likely that some special events 

on trails may actually provide opportunity for complete 

censuses of LERs based on the specific administrative or 

coordination activities associated with the particular events.

One of the major problems in trail visitation estimation 

is that onsite sampling often results in sampled site days 

having low or no visitation, thus yielding no data for 

estimation of the important scale parameters , , and 

. Such low sampling intensity not only results in erratic 

estimates of these parameters with large variability as shown 

in this report, but is the reason why the visitation estimators 

are based on the product of their means instead of the mean 

of their individual daily product.

The model-based approach was used here in an attempt to 

mitigate the effect of small sample sizes on the design-based 

estimator. Results for the parameter estimates reveal several 

justifications for preferring the model-based approach over 

the design-based approach. First, limited resources can 

result in low-sampling intensity for certain strata which 

increases the risk of erratic estimates for the design-based 

approach. This is alleviated to a certain extent with the 

model-based approach because the data are combined, the 

relationship between site-type and use-level is modeled, 

and then the individual strata estimates are obtained from 

the model. Second, the model-based approach smoothes 

the calibration parameter estimates so that inconsistencies 

are eliminated or mitigated. For instance, if a parameter 

increases with increasing use-level for a given site-type, it 

probably exhibits this pattern for the other site-types. The 

design-based approach does not have this property because 

the individual strata estimates are not linked via a common 

model. Third, the standard errors of the parameter estimates 

are substantially smaller with the model-based approach 

because all the data are combined and used jointly in the 

estimation process. Alternatively, the design-based approach 

estimates a stratum’s parameter based only on the data 

observed in that stratum, which results in a smaller sample 

size and, consequently, a larger standard error. 

Despite the advantages of the model-based approach when 

the sampling intensity is low, the design-based approach 

is preferred when adequate sampling is affordable and 

has been achieved. In recreation use studies, this is rarely 

the case. With the design-based approach, the estimate 

for a given stratum is independent of the other strata and 

is capable of reflecting its individual characteristics and 

properties. It does not rely on a model which may or may 

not assume interaction between site-type and use-level. 

Future research will hopefully allow sampling across 

the entire spatial and temporal range of the AT so that 

extrapolation is unnecessary to estimate overall annual 

visitation. Parameter and visitation estimates derived 

from the pilot survey, along with the trailwide site day 

classification which was part of this research, will be 

fundamental to making a future trailwide sampling and 

visitation estimate economically feasible.

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47

List of Acronyms and Abbreviations

AT = Appalachian National Scenic Trail

ATC = Appalachian Trail Conservancy

ATCH = Appalachian Trail Conservancy Headquarters site-type

CI = Confidence intervals

CV = Coefficient of variation

GIS = Geographical Information System

H = High use-level

HF = Harpers Ferry site-type

L = Low use-level

LER = Last-exiting recreationist

M = Medium use-level

MU = Multiple use site-type

NPS =National Park Service

NVUM = National Visitor Use Monitoring

P = Parking site-type

PSU = Primary sampling unit

SE = Standard error

SSU = Secondary sampling unit

TR = Trail/road site-type

TWE = Trailwide extrapolation

USFS = U.S. Forest Service

Appendix A
48

Zarnoch Page 2 of 10 March 10, 2010 

The pilot survey prework spreadsheet consists of all the sites classified into site-types and 

use-levels for the entire 2007 calendar year. The pilot survey actually used only those site 

days from June 1 through August 14, 2007. The site names that correspond to the site 

numbers can be found in table 1. 

Site 

number 

Sitetype Use--

level Begin End Mon. Tues. Wed. Thurs. Fri. Sat. Sun. Holiday 

0 ATCH L 101 330 1 1 1 1 1 1 1 

0 ATCH M 331 430 1 1 1 1 1 

0 ATCH H 331 430 1 1 

0 ATCH M 501 531 1 1 1 1 1 

0 ATCH H 501 531 1 1 1 

0 ATCH H 601 731 1 1 1 1 1 1 1 1 

0 ATCH M 801 930 1 1 1 1 1 1 1 1 

0 ATCH M 1001 1031 1 1 1 1 1 1 

0 ATCH H 1001 1031 1 1 

0 ATCH M 1101 1130 1 1 1 1 1 1 1 1 

0 ATCH L 1201 1231 1 1 1 1 1 1 1 1 

809 TR L 101 1231 1 1 1 1 1 1 1 1 

810 HF L 102 1224 1 1 1 1 1 

810 HF M 102 331 1 1 

810 HF M 1101 1224 1 1 

810 HF H 101 101 1 

810 HF H 401 1031 1 1 

810 HF H 1225 1231 1 1 1 1 1 1 1 

810 HF H 101 1231 1 

811 HF L 102 331 1 1 1 1 1 1 1 

811 HF L 401 1031 1 1 1 1 1 

811 HF L 1101 1224 1 1 1 1 1 1 1 

811 HF M 101 101 1 

811 HF M 401 1031 1 1 

811 HF M 1225 1231 1 1 1 1 1 1 1 

811 HF M 101 1231 1 

812 HF L 101 1231 1 1 1 1 1 1 1 1 

813 HF L 102 1224 1 1 1 1 1 

813 HF M 102 331 1 1 

813 HF M 1101 1224 1 1 

813 HF H 101 101 1 

813 HF H 401 1031 1 1 

813 HF H 1225 1231 1 1 1 1 1 1 1 

813 HF H 101 1231 1 

814 TR L 101 1231 1 1 1 1 1 1 1 1 

816 P L 102 331 1 1 1 1 1 1 1 

816 P L 401 1031 1 1 1 1 1 

816 P L 1101 1224 1 1 1 1 1 1 1 

816 P M 101 101 1 

816 P M 401 1031 1 1 

816 P M 1225 1231 1 1 1 1 1 1 1 

816 P M 101 1231 1 

817 TR L 101 1231 1 1 1 1 1 1 1 1 

819 P L 102 1224 1 1 1 1 1 

819 P M 102 331 1 1 

819 P M 1101 1224 1 1 

819 P H 101 101 1 

819 P H 401 1031 1 1 

continued 

Appendix B
49

Zarnoch Page 3 of 10 March 10, 2010 

The pilot survey prework spreadsheet consists of all the sites classified into site-types and 

use-levels for the entire 2007 calendar year. The pilot survey actually used only those site 

days from June 1 through August 14, 2007. The site names that correspond to the site 

numbers can be found in table 1 (continued) 

Site 

number 

Sitetype Use--

level Begin End Mon. Tues. Wed. Thurs. Fri. Sat. Sun. Holiday 

 

819 P H 1225 1231 1 1 1 1 1 1 1 

819 P H 101 1231 1 

828 MU L 102 331 1 1 1 1 1 1 1 

828 MU L 401 1031 1 1 1 1 1 

828 MU L 1101 1224 1 1 1 1 1 1 1 

828 MU M 101 101 1 

828 MU M 401 1031 1 1 

828 MU M 1225 1231 1 1 1 1 1 1 1 

828 MU M 101 1231 1 

827 MU L 101 1231 1 1 1 1 1 1 1 1 

825 MU L 102 1224 1 1 1 1 1 

825 MU M 102 331 1 1 

825 MU M 1101 1224 1 1 

825 MU H 101 101 1 

825 MU H 401 1031 1 1 

825 MU H 1225 1231 1 1 1 1 1 1 1 

825 MU H 101 1231 1 

829 TR L 101 1231 1 1 1 1 1 1 1 1 

832 P L 101 331 1 1 1 1 1 1 1 

832 P L 401 1031 1 1 1 1 1 

832 P L 1101 1231 1 1 1 1 1 1 1 

832 P M 401 1031 1 1 

832 P M 101 1231 1 

833 TR L 101 1231 1 1 1 1 1 1 1 1 

834 P L 401 430 1 1 1 1 1 1 1 

834 P L 801 1130 1 1 1 1 1 1 1 1 

834 P M 501 731 1 1 1 1 1 1 1 1 

835 P L 101 331 1 1 1 1 1 1 1 

835 P L 401 1031 1 1 1 1 1 

835 P L 1101 1231 1 1 1 1 1 1 1 

835 P M 401 1031 1 1 

835 P M 101 1231 1 

836 P L 101 228 1 1 1 1 1 1 1 

836 P L 301 531 1 1 1 1 1 

836 P L 1001 1031 1 1 1 1 1 

836 P L 1101 1231 1 1 1 1 1 1 1 

836 P L 704 704 1 

836 P L 903 903 1 

836 P L 1122 1122 1 

836 P M 301 531 1 1 

836 P M 1001 1031 1 1 

836 P M 601 930 1 1 1 1 1 1 1 

836 P M 528 528 1 

836 P M 1008 1008 1 

838 TR L 101 1231 1 1 1 1 1 1 1 1 

839 MU L 101 1231 1 1 1 1 1 1 1 1 

841 MU L 101 228 1 1 1 1 1 1 1 1 

841 MU L 301 430 1 1 1 1 1 

841 MU L 901 1031 1 1 1 1 1 

continued 

Appendix B
50

Zarnoch Page 4 of 10 March 10, 2010 

The pilot survey prework spreadsheet consists of all the sites classified into site-types and

use-levels for the entire 2007 calendar year. The pilot survey actually used only those site 

days from June 1 through August 14, 2007. The site names that correspond to the site 

numbers can be found in table 1 (continued) 

Site 

number 

Sitetype Uselevel Begin End Mon. Tues. Wed. Thurs. Fri. Sat. Sun. Holiday 

 

841 MU L 1101 1231 1 1 1 1 1 1 1 1 

841 MU M 301 430 1 1 

841 MU M 501 630 1 1 1 1 1 

841 MU H 501 630 1 1 

841 MU H 701 831 1 1 1 1 1 1 1 

841 MU H 901 1031 1 1 

841 MU H 528 1008 1 

840 MU L 101 1231 1 1 1 1 1 1 1 1 

842 MU L 101 1231 1 1 1 1 1 1 1 1 

844 P L 101 1231 1 1 1 1 1 1 1 1 

846 TR L 101 1231 1 1 1 1 1 1 1 1 

848 TR L 101 1231 1 1 1 1 1 1 1 1 

849 P L 101 228 1 1 1 1 1 1 1 

849 P L 301 531 1 1 1 1 1 

849 P L 1101 1231 1 1 1 1 1 

849 P M 301 531 1 1 

849 P M 601 1031 1 1 1 1 

849 P M 1101 1231 1 1 

849 P H 601 1031 1 1 1 

849 P H 101 1231 1 

853 TR L 101 331 1 1 1 1 1 1 1 

853 TR L 1101 1231 1 1 1 1 1 1 1 

853 TR L 401 1031 1 1 1 1 1 

853 TR M 401 1031 1 1 

853 TR M 401 1031 1 

853 TR M 1122 1122 1 1 1 

857 TR L 101 1231 1 1 1 1 1 1 1 1 

864 P L 101 331 1 1 1 1 1 1 1 

864 P L 401 1031 1 1 1 1 1 

864 P L 1101 1231 1 1 1 1 1 1 1 

864 P M 401 1031 1 1 

864 P M 101 1231 1 

865 P L 101 331 1 1 1 1 1 1 1 

865 P L 401 1031 1 1 1 1 1 

865 P L 1101 1231 1 1 1 1 1 1 1 

865 P M 401 1031 1 1 

865 P M 101 1231 1 

867 TR L 101 331 1 1 1 1 1 1 1 

867 TR L 401 1031 1 1 1 1 1 

867 TR L 1101 1231 1 1 1 1 1 1 1 

867 TR M 401 1031 1 1 

867 TR M 101 1231 1 

869 TR L 101 1231 1 1 1 1 1 1 1 1 

872 P L 101 1231 1 1 1 1 1 1 1 1 

874 TR L 101 1231 1 1 1 1 1 1 1 1 

875 P L 101 331 1 1 1 1 1 1 1 

875 P L 1101 1131 1 1 1 1 1 

875 P L 1201 1231 1 1 1 1 1 1 1 

875 P M 401 531 1 1 1 1 1 1 1 

 

continued 

Appendix B
51

Zarnoch Page 5 of 10 March 10, 2010 

The pilot survey prework spreadsheet consists of all the sites classified into site-types and

use-levels for the entire 2007 calendar year. The pilot survey actually used only those site 

days from June 1 through August 14, 2007. The site names that correspond to the site 

numbers can be found in table 1 (continued) 

Site 

number 

Sitetype Uselevel Begin End Mon. Tues. Wed. Thurs. Fri. Sat. Sun. Holiday 

 

875 P M 601 1031 1 1 1 1 1 

875 P M 1101 1130 1 1 

875 P H 601 1031 1 1 

875 P H 101 1231 1 

878 MU L 101 331 1 1 1 1 1 1 1 

878 MU L 1101 1231 1 1 1 1 1 1 1 1 

878 MU L 401 430 1 1 1 1 1 

878 MU L 1001 1031 1 1 1 1 1 

878 MU M 401 430 1 1 

878 MU M 1001 1031 1 1 1 

878 MU M 501 930 1 1 1 1 1 1 1 1 

881 TR L 101 1231 1 1 1 1 1 1 1 1 

884 TR L 101 1231 1 1 1 1 1 1 1 1 

887 TR L 101 1231 1 1 1 1 1 1 1 1 

888 P L 101 630 1 1 1 1 1 

888 P L 901 1231 1 1 1 1 1 

888 P M 101 630 1 1 

888 P M 701 831 1 1 1 1 1 1 1 

888 P M 901 1231 1 1 

888 P M 101 1231 1 

890 P L 101 331 1 1 1 1 1 1 1 

890 P L 401 1031 1 1 1 1 1 

890 P L 1101 1231 1 1 1 1 1 1 1 

890 P M 401 1031 1 1 

890 P M 101 1231 1 

891 TR L 101 1231 1 1 1 1 1 1 1 1 

893 TR L 101 1231 1 1 1 1 1 1 1 1 

897 P L 101 331 1 1 1 1 1 1 1 

897 P L 401 1031 1 1 1 1 1 

897 P L 1101 1231 1 1 1 1 1 1 1 

897 P M 401 1031 1 1 

897 P M 101 1231 1 

899 TR L 101 430 1 1 1 1 1 1 1 

899 TR L 501 630 1 1 1 1 1 

899 TR L 901 1031 1 1 1 1 1 

899 TR L 1101 1231 1 1 1 1 1 1 1 

899 TR M 501 630 1 1 

899 TR M 701 831 1 1 1 1 1 1 1 

899 TR M 901 1031 1 1 

899 TR M 101 1231 1 

901 P L 101 331 1 1 1 1 1 1 1 

901 P L 401 1031 1 1 1 1 1 

901 P L 1101 1231 1 1 1 1 1 1 1 

901 P M 401 1031 1 1 

901 P M 101 1231 1 

903 P L 101 331 1 1 1 1 1 1 1 

903 P L 401 1031 1 1 1 1 1 

903 P L 1101 1231 1 1 1 1 1 1 1 

903 P M 401 1031 1 1 

 

continued 

Appendix B
52

Zarnoch Page 6 of 10 March 10, 2010 

The pilot survey prework spreadsheet consists of all the sites classified into site-types and

use-levels for the entire 2007 calendar year. The pilot survey actually used only those site 

days from June 1 through August 14, 2007. The site names that correspond to the site 

numbers can be found in table 1 (continued) 

Site 

number 

Sitetype Uselevel Begin End Mon. Tues. Wed. Thurs. Fri. Sat. Sun. Holiday 

 

903 P M 101 1231 1 

904 TR L 101 1231 1 1 1 1 1 1 1 1 

905 P L 101 331 1 1 1 1 1 1 1 

905 P L 401 1031 1 1 1 1 1 

905 P L 1101 1231 1 1 1 1 1 1 1 

905 P M 401 1031 1 1 

905 P M 101 1231 1 

908 TR L 101 1231 1 1 1 1 1 1 1 1 

909 TR L 101 430 1 1 1 1 1 1 1 

909 TR L 501 630 1 1 1 1 1 

909 TR L 901 1031 1 1 1 1 1 

909 TR L 1101 1231 1 1 1 1 1 1 1 

909 TR M 501 630 1 1 

909 TR M 701 831 1 1 1 1 1 1 1 

909 TR M 901 1031 1 1 

909 TR M 101 1231 1 

910 P L 101 331 1 1 1 1 1 1 1 

910 P L 401 1031 1 1 1 1 1 

910 P L 1101 1231 1 1 1 1 1 1 1 

910 P M 401 1031 1 1 

910 P M 101 1231 1 

913 TR L 101 1231 1 1 1 1 1 1 1 1 

914 MU L 101 1231 1 1 1 1 1 1 1 1 

915 MU L 101 1231 1 1 1 1 1 1 1 1 

916 MU L 102 331 1 1 1 1 1 1 1 

916 MU L 401 1031 1 1 1 1 1 

916 MU L 1101 1224 1 1 1 1 1 1 1 

916 MU M 101 101 1 

916 MU M 401 1031 1 1 

916 MU M 1225 1231 1 1 1 1 1 1 1 

916 MU M 101 1231 1 

917 MU L 102 331 1 1 1 1 1 1 1 

917 MU L 401 1031 1 1 1 1 1 

917 MU L 1101 1224 1 1 1 1 1 1 1 

917 MU M 101 101 1 

917 MU M 401 1031 1 1 

917 MU M 1225 1231 1 1 1 1 1 1 1 

917 MU M 101 1231 1 

919 MU L 101 331 1 1 1 1 1 1 1 

919 MU L 401 531 1 1 1 1 1 

919 MU L 901 1130 1 1 1 1 1 

919 MU L 1201 1231 1 1 1 1 1 1 1 

919 MU M 401 531 1 1 

919 MU M 601 831 1 1 1 1 1 

919 MU M 1001 1130 1 1 

919 MU H 601 930 1 1 

919 MU H 101 1231 1 

920 MU L 101 1231 1 1 1 1 1 1 1 1 

921 MU L 101 1231 1 1 1 1 1 1 1 1 

 

continued 

Appendix B
53

Zarnoch Page 7 of 10 March 10, 2010 

The pilot survey prework spreadsheet consists of all the sites classified into site-types and

use-levels for the entire 2007 calendar year. The pilot survey actually used only those site 

days from June 1 through August 14, 2007. The site names that correspond to the site 

numbers can be found in table 1 (continued) 

Site 

number 

Sitetype Uselevel Begin End Mon. Tues. Wed. Thurs. Fri. Sat. Sun. Holiday 

 

922 MU L 101 1231 1 1 1 1 1 1 1 1 

923 TR L 101 430 1 1 1 1 1 1 1 

923 TR L 501 630 1 1 1 1 1 

923 TR L 901 1031 1 1 1 1 1 

923 TR L 1101 1231 1 1 1 1 1 1 1 

923 TR M 501 630 1 1 

923 TR M 701 831 1 1 1 1 1 1 1 

923 TR M 901 1031 1 1 

923 TR M 101 1231 1 

924 TR L 101 430 1 1 1 1 1 1 1 

924 TR L 501 630 1 1 1 1 1 

924 TR L 901 1031 1 1 1 1 1 

924 TR L 1101 1231 1 1 1 1 1 1 1 

924 TR M 501 630 1 1 

924 TR M 701 831 1 1 1 1 1 1 1 

924 TR M 901 1031 1 1 

924 TR M 101 1231 1 

925 TR L 101 430 1 1 1 1 1 1 1 

925 TR L 501 630 1 1 1 1 1 

925 TR L 901 1031 1 1 1 1 1 

925 TR L 1101 1231 1 1 1 1 1 1 1 

925 TR M 501 630 1 1 

925 TR M 701 831 1 1 1 1 1 1 1 

925 TR M 901 1031 1 1 

925 TR M 101 1231 1 

926 TR L 101 1231 1 1 1 1 1 1 1 1 

927 TR L 101 1231 1 1 1 1 1 1 1 1 

928 TR L 101 1231 1 1 1 1 1 1 1 1 

929 TR L 101 1231 1 1 1 1 1 1 1 1 

930 TR L 101 1231 1 1 1 1 1 1 1 1 

931 TR L 101 1231 1 1 1 1 1 1 1 1 

932 TR L 101 1231 1 1 1 1 1 1 1 1 

933 TR L 101 430 1 1 1 1 1 1 1 

933 TR L 501 630 1 1 1 1 1 

933 TR L 901 1031 1 1 1 1 1 

933 TR L 1101 1231 1 1 1 1 1 1 1 

933 TR M 501 630 1 1 

933 TR M 701 831 1 1 1 1 1 1 1 

933 TR M 901 1031 1 1 

933 TR M 101 1231 1 

934 TR L 101 1231 1 1 1 1 1 1 1 1 

935 TR L 101 1231 1 1 1 1 1 1 1 1 

937 P L 101 331 1 1 1 1 1 1 1 

937 P L 401 1031 1 1 1 1 1 

937 P L 1101 1231 1 1 1 1 1 1 1 

937 P M 401 1031 1 1 

937 P M 101 1231 1 

938 P L 101 331 1 1 1 1 1 1 1 

938 P L 401 1031 1 1 1 1 1 

 

continued 

Appendix B
54

Zarnoch Page 8 of 10 March 10, 2010 

The pilot survey prework spreadsheet consists of all the sites classified into site-types and

use-levels for the entire 2007 calendar year. The pilot survey actually used only those site 

days from June 1 through August 14, 2007. The site names that correspond to the site 

numbers can be found in table 1 (continued) 

Site 

number 

Sitetype Uselevel Begin End Mon. Tues. Wed. Thurs. Fri. Sat. Sun. Holiday 

 

938 P L 1101 1231 1 1 1 1 1 1 1 

938 P M 401 1031 1 1 

938 P M 101 1231 1 

942 TR L 101 430 1 1 1 1 1 1 1 

942 TR L 501 630 1 1 1 1 1 

942 TR L 901 1031 1 1 1 1 1 

942 TR L 1101 1231 1 1 1 1 1 1 1 

942 TR M 501 630 1 1 

942 TR M 701 831 1 1 1 1 1 1 1 

942 TR M 901 1031 1 1 

942 TR M 101 1231 1 

946 TR L 101 1231 1 1 1 1 1 1 1 1 

948 TR L 101 1231 1 1 1 1 1 1 1 1 

949 P L 101 331 1 1 1 1 1 1 1 

949 P L 401 630 1 1 1 1 1 

949 P L 901 1031 1 1 1 1 1 

949 P L 1101 1231 1 1 1 1 1 1 1 

949 P M 401 630 1 1 

949 P M 701 831 1 1 1 1 1 1 1 

949 P M 901 1031 1 1 

949 P M 101 1231 1 

950 P L 101 331 1 1 1 1 1 1 1 

950 P L 401 630 1 1 1 1 1 

950 P L 901 1031 1 1 1 1 1 

950 P L 1101 1231 1 1 1 1 1 1 1 

950 P M 401 630 1 1 

950 P M 701 831 1 1 1 1 1 1 1 

950 P M 901 1031 1 1 

950 P M 101 1231 1 

951 P L 101 1231 1 1 1 1 1 1 1 1 

953 MU L 101 430 1 1 1 1 1 1 1 1 

953 MU L 801 1231 1 1 1 1 1 1 1 1 

953 MU M 501 731 1 1 1 1 1 1 1 1 

954 MU L 101 331 1 1 1 1 1 1 1 

954 MU L 401 630 1 1 1 1 1 

954 MU L 901 1031 1 1 1 1 1 

954 MU L 1101 1231 1 1 1 1 1 1 1 

954 MU M 401 630 1 1 

954 MU M 701 831 1 1 1 1 1 1 1 

954 MU M 901 1031 1 1 

954 MU M 101 1231 1 

955 MU L 101 331 1 1 1 1 1 1 1 

955 MU L 401 531 1 1 1 1 1 

955 MU L 901 1130 1 1 1 1 1 

955 MU L 1201 1231 1 1 1 1 1 1 1 

955 MU M 401 531 1 1 

955 MU M 601 831 1 1 1 1 1 

955 MU M 1001 1130 1 1 

955 MU H 601 930 1 1 

 

continued 

Appendix B
55

Zarnoch Page 9 of 10 March 10, 2010 

The pilot survey prework spreadsheet consists of all the sites classified into site-types and

use-levels for the entire 2007 calendar year. The pilot survey actually used only those site 

days from June 1 through August 14, 2007. The site names that correspond to the site 

numbers can be found in table 1 (continued) 

Site 

number 

Sitetype Uselevel Begin End Mon. Tues. Wed. Thurs. Fri. Sat. Sun. Holiday 

 

955 MU H 101 1231 1 

957 MU L 101 331 1 1 1 1 1 1 1 

957 MU L 401 630 1 1 1 1 1 

957 MU L 901 1031 1 1 1 1 1 

957 MU L 1101 1231 1 1 1 1 1 1 1 

957 MU M 401 630 1 1 

957 MU M 701 831 1 1 1 1 1 1 1 

957 MU M 901 1031 1 1 

957 MU M 101 1231 1 

958 TR L 101 430 1 1 1 1 1 1 1 

958 TR L 501 630 1 1 1 1 1 

958 TR L 901 1031 1 1 1 1 1 

958 TR L 1101 1231 1 1 1 1 1 1 1 

958 TR M 501 630 1 1 

958 TR M 701 831 1 1 1 1 1 1 1 

958 TR M 901 1031 1 1 

958 TR M 101 1231 1 

959 TR L 101 1231 1 1 1 1 1 1 1 1 

961 TR L 101 1231 1 1 1 1 1 1 1 1 

962 TR L 101 1231 1 1 1 1 1 1 1 1 

963 TR L 101 630 1 1 1 1 1 1 1 

963 TR L 901 1231 1 1 1 1 1 1 1 

963 TR M 701 831 1 1 1 1 1 1 1 

963 TR M 101 1231 1 

965 P L 101 1231 1 1 1 1 1 1 1 1 

967 P L 101 1231 1 1 1 1 1 1 1 1 

970 P L 101 1231 1 1 1 1 1 1 1 1 

973 TR L 101 1231 1 1 1 1 1 1 1 1 

975 P L 101 1231 1 1 1 1 1 1 1 1 

981 TR L 101 1231 1 1 1 1 1 1 1 1 

982 TR L 101 1231 1 1 1 1 1 1 1 1 

984 P L 101 1231 1 1 1 1 1 1 1 1 

987 TR L 101 630 1 1 1 1 1 1 1 1 

987 TR L 901 1231 1 1 1 1 1 1 1 1 

987 TR M 701 831 1 1 1 1 1 1 1 1 

988 TR L 101 430 1 1 1 1 1 1 1 

988 TR L 501 1031 1 1 1 1 1 

988 TR L 1101 1231 1 1 1 1 1 1 1 

988 TR M 501 1031 1 1 

988 TR M 101 1231 1 

993 TR L 101 1231 1 1 1 1 1 1 1 1 

994 P L 101 1231 1 1 1 1 1 1 1 1 

995 P L 101 1231 1 1 1 1 1 1 1 1 

998 MU L 101 1231 1 1 1 1 1 1 1 1 

999 MU L 101 331 1 1 1 1 1 1 1 

999 MU L 401 531 1 1 1 1 1 

999 MU L 901 1130 1 1 1 1 1 

999 MU L 1201 1231 1 1 1 1 1 1 1 

999 MU M 401 531 1 1 

 

continued 

Appendix B
56

Zarnoch Page 10 of 10 March 10, 2010 

The pilot survey prework spreadsheet consists of all the sites classified into site-types and

use-levels for the entire 2007 calendar year. The pilot survey actually used only those site 

days from June 1 through August 14, 2007. The site names that correspond to the site 

numbers can be found in table 1 (continued) 

Site 

number 

Sitetype Uselevel Begin End Mon. Tues. Wed. Thurs. Fri. Sat. Sun. Holiday 

 

999 MU M 601 831 1 1 1 1 1 

999 MU M 1101 1130 1 1 

999 MU H 601 1031 1 1 

999 MU H 101 1231 1 

1000 MU L 101 331 1 1 1 1 1 1 1 

1000 MU L 1101 1130 1 1 1 1 1 

1000 MU L 1201 1231 1 1 1 1 1 1 1 

1000 MU M 401 531 1 1 1 1 1 1 1 

1000 MU M 601 1031 1 1 1 1 1 

1000 MU M 1101 1130 1 1 

1000 MU H 601 1031 1 1 

1000 MU H 101 1231 1 

1001 MU L 101 1231 1 1 1 1 1 1 1 1 

1002 MU L 101 1231 1 1 1 1 1 1 1 1 

1003 TR L 101 1231 1 1 1 1 1 1 1 1 

1004 TR L 101 1231 1 1 1 1 1 1 1 1 

1005 P L 101 1231 1 1 1 1 1 1 1 1 

1007 P L 101 1231 1 1 1 1 1 1 1 1 

1009 TR L 101 1231 1 1 1 1 1 1 1 1 

1010 TR L 101 1231 1 1 1 1 1 1 1 1 

1011 TR L 101 1231 1 1 1 1 1 1 1 1 

1015 TR L 101 531 1 1 1 1 1 1 1 

1015 TR L 801 1231 1 1 1 1 1 1 1 

1015 TR L 101 1231 1 

1015 TR M 601 731 1 1 1 1 1 1 1 

1016 P L 101 1231 1 1 1 1 1 1 1 1 

1019 TR L 101 1231 1 1 1 1 1 1 1 1 

Note: ATCH = Appalachian Trail Conservancy Headquarters; TR = trail/road; HF = Harpers Ferry; P = parking; 

MU = multiple use; L= low; M = medium; H = high..

Appendix B


Zarnoch, Stanley J.; Bowker, J.M.; Cordell, H. Ken [and others]. 

2011. Appalachian National Scenic Trail pilot survey. Gen. Tech. 

Rep. SRS–143. Asheville, NC: U.S. Department of Agriculture 

Forest Service, Southern Research Station. 56 p.

Visitation statistics on the Appalachian National Scenic Trail (AT) are important 

for management and Federal Government reporting purposes. However, no survey 

methodology has been developed to obtain accurate trailwide estimates over linear 

trails that traverse many hundreds of back-country miles. This research develops 

a stratified random survey design which utilizes two survey instruments, exit-site 

tallies and a survey questionnaire, to obtain visitation estimates on a portion of the 

AT. The design identifies three components (standard site days, augmented site 

days, and special events) which can be used to subdivide the sampling frame into 

estimator types that lead to more efficient sampling and estimation processes. In 

addition, design-based and model-based approaches are used to obtain estimates for 

comparison purposes.

The survey was performed from June 1 through August 14, 2007, on a 109-mile 

stretch of the AT from Harpers Ferry, WV, to 10 trail miles north of Boiling Springs, 

PA, at the Scott Farm. Visitation estimates were 66,967 for the design-based 

approach and 70,912 for the model-based approach, with coefficients of variation 

of 23 and 16 percent, respectively. Individual strata-level visitation estimates were 

quite variable and differed substantially between the two approaches. 

An extrapolation to the entire trail for the whole year was performed by developing 

an appropriate sampling frame from which the strata weights could be obtained. 

Using the model-based approach and assuming the survey data were representative, 

the 2007 annual visitation extrapolation for the entire trail was 1,948,701 with a 

coefficient of variation of 20 percent. 

Keywords: Design-based estimator, Lincoln-Petersen estimator, mark-recapture 

estimator, model-based estimator, recreation trail use estimation.
The Forest Service, United States Department 

of Agriculture (USDA), is dedicated to the 

principle of multiple use management of the

Nation’s forest resources for sustained yields of wood, water, 

forage, wildlife, and recreation. Through forestry research, 

cooperation with the States and private forest owners, and 

management of the National Forests and National Grasslands, 

it strives—as directed by Congress—to provide increasingly 

greater service to a growing Nation.

The USDA prohibits discrimination in all its programs and 

activities on the basis of race, color, national origin, age, 

disability, and where applicable, sex, marital status, familial 

status, parental status, religion, sexual orientation, genetic 

information, political beliefs, reprisal, or because all or part 

of an individual’s income is derived from any public assistance 

program. (Not all prohibited bases apply to all programs.) 

Persons with disabilities who require alternative means for 

communication of program information (Braille, large print, 

audiotape, etc.) should contact USDA’s TARGET Center at 

(202) 720-2600 (voice and TDD).

To file a complaint of discrimination, write to USDA, 

Director, Office of Civil Rights, 1400 Independence Avenue, 

SW, Washington, D.C. 20250-9410, or call (800) 795-3272 

(voice) or (202) 720-6382 ( TDD). USDA is an equal 

opportunity provider and employer.