REPORT ON THE NATIONAL SURVEY

OF LEAD-BASED PAINT IN HOUSING

Base Report

This work was conducted under

HUD Contract Number HC-5848 and

EPA Contract Numbers 68-D9-0174, 68-D2-0139 and 68-D3-0011

June, 1995
iii

ACKNOWLEDGMENTS

Westat would like to acknowledge the many people that contributed to this study. The data

analysis and report writing work was directed by Manie Chen, Work Assignment Manager, Office of

Pollution Prevention and Toxics (OPPT), U.S. Environmental Protection Agency (EPA), Phil Robinson,

Section Head, Technical Programs Branch, and Cindy Stroup, Chief, Technical Programs Branch,

OPPTS, EPA.

Westat appreciates the support and guidance of staff from EPA, the U.S. Department of

Housing and Urban Development (HUD), and Cox Associates for reviewing the research and providing

technical guidance and input. In addition to the above, they include: John Schwemberger, Bradley

Schultz, and Joseph Breen of EPA; Stevenson Weitz, Ellis Goldman, Ron Morony and Art Newburg of

HUD; and Arnold Greenland and David Cox of Cox Associates.

Westat carried out the research for this study and wrote this report. Key members of the

Westat research team include: Robert Clickner, Project Director and Co-Principal Investigator; John

Rogers, Co-Principal Investigator; Victoria Albright, Field Director; Richard Rinehart, Research

Associate; Charles Carusi, Research Associate; Edward Bryant, Statistician; Janice Machado, Research

Associate; William Devlin, Research Associate; Stephen Dietz, Corporate Officer, John Michael,

Statistician; Ben Tepping, Statistician; Valerija Smith, Statistician; George Fisher, Programmer; David

Lowe, Programmer; Helen Powell, Programmer; Joyce Powell, Programmer; Angela HoSang, Research

Assistant; Mary Madigan, Research Associate; Debbie Kitchell, Editor; Gudrun Tomasson, Research

Assistant; Michael Vendetti, Research Assistant; and Brian Dingwall, Research Assistant.

The national survey of lead-based paint in housing was conducted for HUD by Westat, Inc.,

in affiliation with Dewberry and Davis and KTA-Tator, under HUD Contract HC-5848. Initial data

analyses were conducted by Westat, Inc. in affiliation with Speedwell, Inc., under the same contract. The

additional analyses reported in this report were conducted by Westat under EPA Contracts 68-D9-0174,

68-D2-0139 and 68-D3-0011.
iv

TABLE OF CONTENTS

Chapter Page

ACKNOWLEDGMENTS..................................................................................................... i

EXECUTIVE SUMMARY ................................................................................................... v

1 INTRODUCTION ............................................................................................ 1-1

1.1 Background.......................................................................................... 1-1

1.2 Report Organization............................................................................. 1-3

1.3 Objectives of National Survey of Lead-Based Paint in Housing.......... 1-3

1.4 Lead Standards and Guidelines............................................................ 1-4

2 NATIONAL ESTIMATES OF PREVALENCE .............................................. 2-1

2.1 Major Findings and Discussion............................................................ 2-1

2.2 Lead Paint Hazard in Private Housing ................................................. 2-2

2.3 Lead Paint Hazard in Public Housing .................................................. 2-9

3 RESEARCH DESIGN...................................................................................... 3-1

3.1 Sample Design ..................................................................................... 3-1

3.2 Inspection Protocol .............................................................................. 3-4

3.3 Environmental Sampling Protocols...................................................... 3-5

3.4 Quality Assurance................................................................................ 3-6

3.4.1 Measures to Enhance Response Rates..................................... 3-6

3.4.2 Quality Assurance for MAP/XRF Data................................... 3-6

3.4.3 Field Quality Assurance Measures.......................................... 3-7

3.5 Limitations of the Study Design .......................................................... 3-7

4 SOURCES OF ERROR IN THE NATIONAL SURVEY DATA .................... 4-1

4.1 Response Rates and Potential for Non-Response Bias......................... 4-1

4.1.1 Private Housing....................................................................... 4-1

4.1.2 Public Housing........................................................................ 4-2

4.2 MAP/XRF Measurement Bias ............................................................. 4-3

4.3 Classification Error Due to MAP/XRF Measurement Variation.......... 4-3

4.4 Classification Error Due to Dwelling Unit Sampling Procedures ........ 4-4

4.5 Impact on the National Estimates of Prevalence.................................. 4-4
v

TABLE OF CONTENTS (continued)

Chapter Page

5 CONCLUSIONS .............................................................................................. 5-1

5.1 Major Conclusions............................................................................... 5-1

5.1.1 Study Findings ........................................................................ 5-1

5.1.2 Impact of Measurement Error and Lead Loading Variation

on the Data Analysis ............................................................... 5-1

5.1.3 Use of the Spectrum Analyzer MAP/XRF .............................. 5-2

5.2 Additional Conclusions and Recommendations................................... 5-2

List of Tables

Table Page

2-1 Estimated Number of Privately Owned Occupied Housing Units

Built Before 1980 with Lead-Based Paint, by Selected Characteristics

(Paint Lead Concentration > = 1.0 mg/sq cm) .................................................................... 2-3

2-2 Estimated Number and Percent of Public Housing Units Built Before

1980 with Lead-Based Paint, by Selected Characteristics

(Paint Lead Concentration > = 1.0 mg/sq cm)..................................................................... 2-10

3-1 National Distribution of Dwelling Units Built Before 1980 ............................. 3-2

3-2 Distribution of Completed Inspections by Construction Year and

Dwelling Unit Type .......................................................................................... 3-2

4-1 National Response, Contact, and Eligibility Rates at Each Data

Collection Stage................................................................................................ 4-2

List of Figures

Figure Page

2-1 Prevalence of Lead-Based Paint by Location in Privately Owned

Occupied Housing Units................................................................................... 2-4

2-2 Estimated Percent of Privately Owned Housing Units with Dust

and Soil Lead Exceeding Guidelines by Construction Year ............................. 2-5

2-3 Number of Privately Owned Housing Units with Interior Dust

Lead Levels Above Guidelines by Presence and Condition of

Lead-Based Paint (LBP) ................................................................................... 2-6

2-4 Number of Privately Owned Housing Units with Lead in Soil

by Presence and Condition of Exterior Lead-Based Paint ................................ 2-7

2-5 Average Amount of Lead-Based Paint (LBP) Per Housing Unit

on Interior Surfaces by Painted Component for Privately

Owned Housing Units (LBP Concentration > = 1.0 mg/sg cm)......................................... 2-8
vi

TABLE OF CONTENTS (continued)

List of Figures (continued)

Figure Page

2-6 Average Amount of Lead-Based Paint (LBP) Per Privately Owned

Housing Unit on Exterior Surfaces by Painted Component

(LBP Concentration > = 1.0 mg/sg cm)............................................................................. 2-8

2-7 Amounts of Lead-Based Paint by Location and Construction Year

for Privately Owned Housing Units (LBP Concentration > = 1.0 mg/sg cm).................... 2-11

2-8 Geometric Mean Paint Lead Loadings in Privately Owned Housing

Units by Location and Construction Year (LBP Concentration > = 1.0 mg/sg cm)........... 2-11

2-9 Percent of Public Housing Units with Lead-Based Paint (LBP)

by Location (LBP Concentration > = 1.0 mg/sg cm)......................................................... 2-12

2-10 Average Amounts of Lead-Based Paint (LBP) per Public Housing

Unit on Interior Surfaces by Architectural Component

(LBP Concentration > = 1.0 mg/sg cm)............................................................................. 2-13

2-11 Average Amount of Lead-Based Paint (LBP) in Publicly Owned

Housing Units on Exterior Surfaces by Architectural Component

(LBP Concentration > = 1.0 mg/sg cm)............................................................................. 2-13

2-12 Geometric Mean Paint Lead Loadings in Publicly Owned Housing

Units by Location and Construction Year (LBP Concentration > = 1.0 mg/sg cm)........... 2-14
v

EXECUTIVE SUMMARY

Lead is a powerful toxin that attacks the central nervous system and is particularly damaging to the

developing nervous systems of young children. High levels of lead in the blood can result in convulsions,

mental retardation, and even death. Further, recent medical research has found that low levels of lead

exposure have more serious health consequences that previously thought. Effects include reductions in

intelligence and short-term memory, slower reaction times, and poorer hand-eye coordination.1

Although there are many sources of lead in the environment, including drinking water, food,

emissions from gasoline combustion, and industrial emissions, it is clear that lead-based paint plays a

major role in high blood lead levels. Recent research indicates that dust and soil may be the most

significant pathway for low-level lead exposure, and that lead-based paint is an important source of

household dust lead.2,3

The 1987 amendments to the Lead-Based Paint Poisoning Prevention Act required the Secretary of

Housing and Urban Development (HUD) to prepare and transmit to Congress "a comprehensive and

workable plan" for the abatement of lead-based paint in housing and "an estimate of the amount,

characteristics and regional distribution of housing in the United States that contains lead-based paint

hazards at differing levels of contamination." In response to this mandate, HUD sponsored a national

survey of lead-based paint in housing and delivered a Report to Congress on a Comprehensive and

Workable Plan for the Abatement of Lead-Based Paint in Privately Owned Housing in December, 1990.

The Comprehensive and Workable Plan report was completed under a tight, Congressionally mandated

schedule and focused on motivating, developing and presenting the comprehensive plan required by

Congress. As such, it only reported the estimates of the extent of lead-based paint in housing required by

Congress and provided a brief description of the survey methodology.

This report, sponsored by the Environmental Protection Agency, is a comprehensive technical report

on the HUD-sponsored national survey of lead-based paint in housing. It provides a detailed description of

the survey methodology. It reports on wide ranging analyses of the national survey data. It reports revised

estimates of the extent of lead-based paint in housing, based on a thorough investigation of the multiple

sources of error - variability and bias - in the data. These error sources include nonresponse biases,

sampling variability between housing units, sampling variability within housing units, X-ray fluorescence

device (XRF) measurement error, and laboratory analysis error. The analysis underlying the estimates

presented in the Comprehensive and Workable Plan (CWP) report incorporated only sampling variability

between housing units.

Extent of Lead-based Paint in Housing - Revised Estimates

The number of housing units classified as having lead-based paint depends on the definition

employed to classify a housing unit as having lead-based paint. The definition used here classifies a home

as having lead-based paint if the measured lead concentration on any painted surface is 1.0 mg/cm2, or

greater.

 

1

Fowler, Bruce et al, "Measuring Lead Exposure in Infants, Children, and Other Sensitive Populations," National Academy Press, Washington,

D.C.

2

Bornschein R.L., Hammond P. B., Dietrich K. N., Succop P., Krafft K., Clark S., Berger O., Pearson D., and Que Hee S. (1985). The Cincinnati

prospective study of low-level lead exposure and its effects on child development: Protocol and status report. Environmental Research 38, 4-

18.

3

Bornschein R.L., Succop P. A., Dietrich K. N., Clark C. S., Hee Q. S. and Hammond P. B. (1985). The influence of social and environmental

factors on dust lead, hand lead, and blood lead levels in young children. Environmental Research 38, 108-118.
vi

As reported in the CWP report, lead-based paint is widespread in housing. The revised estimate is

that 64 million homes (± 7 million)4

, 83 percent (± 9%) of the privately owned housing units built before

1980, have lead-based paint somewhere in the building. (Fifty-seven million (± 5 million) homes, or 74

percent (± 6%), were reported in the CWP.) Twelve million (± 1 million) of these homes are occupied by

families with children under the age of seven years old. An estimated 49 million (± 7 million) privately

owned homes have lead-based paint in their interiors. There are no statistically significant differences in

the prevalence of lead-based paint by type of housing, market value of the home, amount of rent payment,

household income, or geographic region.

Seventeen percent of the pre-1980 housing stock have dust lead levels in excess of the federal

guidelines5

, independent of the presence or absence of lead-based paint. However, excessive dust lead

levels are associated with the presence of damaged lead-based paint. Fourteen million homes, 19 percent

of the pre-1980 housing stock, have more than five square feet of damaged lead-based paint. Nearly half of

them (47 percent) have excessive dust lead levels.

Excessive soil lead levels6

 are also associated with the presence of damaged lead-based paint. While

21 percent of all pre-1980 homes have excessive soil lead levels, nearly half of the 10 million homes with

non-intact lead-based paint on exterior walls have excessive soil lead levels.

Although a large majority of pre-1980 homes have lead-based paint, most of them have relatively

small areas of it. The average privately-owned housing unit with lead-based paint has an estimated 601

square feet of it on interior surfaces and 869 square feet on exterior surfaces. Over half of the leaded paint

is on walls, ceilings, and floors. (For comparison, the walls in a room 10' by 12', with an 8' ceiling, have

an area of 352 square feet.) The amounts of lead-based paint per housing unit vary with the age of the

dwelling unit. Pre-1940 units have, on average, about three times as much lead-based paint as units built

between 1960 and 1979.

Lead paint is even more widespread in public housing; 86 percent (± 8%) of all pre-1980 public

housing family units have lead-based paint somewhere in the building. While most public housing units

have some lead-based paint, most of them have small areas of surfaces covered with it. The average public

housing unit with lead-based paint has an estimated 367 square feet on interior surfaces and 133 square

feet on exterior surfaces. Most of the interior lead-based paint is on walls, while very little of the exterior

walls are painted.

Survey Methodology

The objective of the national survey of lead-based paint in housing was to obtain data for estimating:

(1) the number of housing units with lead-based paint; (2) the surface area of lead-based paint in housing,

to develop an estimate of national abatement costs; (3) the condition of the paint; (4) the prevalence of lead

in dust in housing units and in soil around the perimeter of residential structures; and (5) the characteristics

of housing with varying levels of potential hazard, to examine possible priorities for abatement.

The study population consisted of nearly all housing in the United States constructed before 1980.

Vacant housing, group quarters, Alaska and Hawaii were excluded for operational reasons. Newer houses

 

4

The numbers in parentheses are 95% confidence intervals.

5

The federal guidelines vary with the location of the dust: 200 micrograms of lead per square foot for floor samples, 500 μg/sq ft for window sills

and 800 μg/sq ft for window wells.

6

EPA interim guidelines for soil lead action levels are 500 ppm for residential soil associated with Superfund sites.
vii

were presumed to be lead-free because, in 1978, the Consumer Product Safety Commission banned the sale

of lead-based paint to consumers and the use of such paint in residences. The survey was conducted

between December 1989 and March 1990 in 30 counties across the 48 contiguous states, selected to

represent the entire United States housing stock, both public and privately-owned. The total sample size is

381 dwelling units, 284 privately owned and 97 publicly owned. The sample was small, but it provided

estimates that were sufficiently precise to develop the CWP for private and public housing.

Within each housing unit, two rooms were randomly selected for inspection; one room with

plumbing (wet) and one room without plumbing (dry). In each of these two rooms, the field technicians

inventoried painted surfaces, measured their dimensions, and assessed the condition of the paint; they

measured the lead concentration in randomly selected painted surfaces; and they gathered samples of dust.

Since not all rooms in a dwelling unit were inspected, it is possible to miss lead-based paint when it

is really present somewhere else in the dwelling unit. To reduce the chances of misclassifying a dwelling

unit with lead-based paint as lead-free, additional lead readings, termed purposive readings, were taken on

surfaces that, in the opinion of the field technicians, were most likely to have lead-based paint. In some

dwelling units, these additional purposive samples did, indeed, find lead-based paint in dwelling units where

no lead-based paint had been found in the randomly selected rooms.

Exterior painted surfaces were inventoried and measured and lead readings taken according to

protocols similar to those used in the interior. Soil samples were also taken at selected locations around the

building exterior. Common areas were also sampled and inspected.

Lead in paint measurements were made with portable Scitec MAP-3 spectrum analyzer XRF devices

(MAP/XRFs), which NIST had determined to be more accurate and more precise than the direct-reading

XRFs used in earlier surveys. Although the MAP/XRFs were an improvement over the earlier directreading XRFs, they still had limitations. In particular, MAP/XRF measurements made over brick or

concrete were less accurate and less precise than those made over wood or plaster. These limitations

notwithstanding, portable MAP/XRF technology was used because the survey included occupied dwellings

where it was not feasible to take paint scrapings for laboratory analysis.

Data were collected on lead in dust and soil in a number of locations in each sampled dwelling unit.

Dust samples were collected by vacuuming randomly selected floor locations, window sills and window

wells in the wet room and again in the dry room. In addition, a dust sample was collected from the floor

just inside the main entrance to the dwelling unit. Soil samples were taken outside the main entrance to the

building, at a selected location along the drip line of the sampled exterior painted surface, and at a remote

location away from the building but still on the property. Dust and soil samples were analyzed for lead

concentration.

Analyses of the Sources of Error

Nonresponse analysis. An analysis was conducted of the private housing nonresponse in the

national survey to estimate the potential for nonresponse bias. This analysis was necessary because

intrusive studies that impose significant burdens on the respondents tend to have lower response rates than

less burdensome studies and, therefore greater potential for nonresponse biases. In this survey, 53 percent

of the homes asked to permit the inspection visits cooperated fully with the study. The nonresponse

analyses did not reveal any evidence of potential non-response biases associated with ethnicity, building

age, or family income. There were statistically significant associations between the response rates and

monthly rent in tenant-occupied housing units and current market value in owner-occupied housing; the

lower ends of both distributions were somewhat under represented. There was a strong positive correlation

between inspected housing units in the same census block with respect to the presence of lead in paint, dust,

and soil. On balance, these findings suggest that the potential bias due to nonresponse is likely to be small.
viii

Correction for measurement bias. The MAP/XRF measurement equipment used to detect and

quantify lead in paint tended to yield readings that were biased, i.e., systematically different from the actual

lead concentrations measured. Quality assurance (QA) data collected daily during the national survey field

period permitted the estimation of the MAP/XRF bias. MAP/XRF readings were made on shims of known

lead concentration placed over selected substrate materials. A shim is a piece of hard paper painted with

lead-based paint. There were four substrate materials, wood, drywall, steel, and concrete, selected to

represent the typical range of substrate materials encountered in residential construction. Statistical

techniques were applied to the QA data to develop calibration equations for adjusting the MAP/XRF

readings for measurement bias. The MAP/XRF readings taken in the housing units were therefore adjusted

to statistically correct for measurement bias.

Correction for misclassification errors. There are two major factors that induce misclassification

errors. First, the MAP/XRF equipment also has random variability in its measurements. This variation

can induce a classification bias, that is, a bias in the estimated prevalence of housing units with lead-based

paint. Second, the protocol for inspecting a housing unit for lead-based paint provided for sampling

painted surfaces for MAP/XRF measurement, rather than measuring the lead content of every painted

surface in the housing unit. Under this inspection protocol, it is possible for a housing unit to have some

surfaces with lead-based paint, other painted surfaces without lead-based paint, and only the lead-free

surfaces selected for MAP/XRF measurement. Such housing units would be incorrectly classified as not

having lead-based paint.

To adjust for these classification biases, the distribution of lead concentrations on the untested

painted surfaces, in the sampled rooms and in the unsampled rooms, in each household was simulated. (No

applicable, adequate data set existed to permit the direct estimation of these biases.) This extension from

the measured surfaces to all surfaces in the unit was based on (1) data on the number of rooms in the unit,

(2) data on the number of surfaces per room, and (3) assumptions about the relationship of the lead

concentrations on unmeasured surfaces to those on the sampled and measured surfaces. The model was

observed to be consistent with the National Survey data. The misclassification rates were estimated for the

simulated housing units, and used to adjust the prevalence estimates accordingly.

Impact on the national survey findings. All findings on the lead hazard in homes reported

elsewhere in this report incorporate the results of this error analyses. That is, the raw MAP/XRF readings

have been statistically corrected for measurement bias and the misclassifications due to measurement

variation and sampling within dwelling units have been corrected. The national estimate of prevalence of

lead-based paint in privately-owned housing is 83 percent. Without the statistical corrections described

above, the estimate would have been 74 percent.
1-1

1. INTRODUCTION

The National Survey of Lead-Based Paint in Housing was conducted under the sponsorship of the

Department of Housing and Urban Development to provide basic data for comprehensive and workable

plans (CWPs) for the prompt and cost-effective inspection and abatement of lead-based paint hazards in

private and public housing. The CWPs were required by the Lead-Based Paint Poisoning Prevention Act

(LPPPA), as amended by Section 566 of the Housing and Community Development Act of 1987.1

 The

CWP for private housing was issued to Congress in December, 1990.2

 The CWP for public housing is

forthcoming.

1.1 Background

This section presents the background for the national survey. It briefly describes the data available

prior to the national survey on lead-based paint hazards.

Previous Surveys

There were four notable surveys of lead-based paint in housing before the national survey. Three

local surveys, in Washington, D.C., Pittsburgh, and Phoenix, were conducted in the mid-1970s, and one

national survey of public housing was carried out in the 1980s.

The Washington, DC, survey, conducted in 1973 by the National Bureau of Standards (now the

National Institute of Standards and Technology [NIST]) had a sample of 233 housing units representing

the city of Washington.3

 This survey also acted as a HUD-sponsored field test for a Pittsburgh survey

conducted a year later.

The Pittsburgh survey, conducted in 1974 and 1975 by the Allegheny County (PA) Health

Department for the National Bureau of Standards under HUD sponsorship, is by far the largest study of its

type ever conducted. The survey completed inspections in approximately 3,300 housing units from the

entire Pittsburgh urban area.4

The Phoenix survey, conducted in 1976 by the Arizona Department of Health Services, had a

sample of 268 units. The sample represented a single Phoenix Census tract that was chosen because of a

high number of both pre-1940 units and children under five years old.5

 

1

Amendment in Section 566 of the Housing and Community Development Act of 1987 (Public Law 100-242).

2

U.S. Department of Housing and Urban Development, Office of Policy Development and Research (1990), Comprehensive and Workable Plan

for the Abatement of Lead-Based Paint in Privately Owned Housing: Report to Congress.

3

Hall, William; and Ayers, Tyrone (1974), Survey Plans and Data Collection and Analysis Methodologies: Results of a Pre-Survey for the

Magnitude and Extent of the Lead-Based Paint Hazard in Housing (NBSIR 74-426), U.S. Department of Commerce, National Bureau of

Standards.

4

Shier, Douglas R.; and Hall, William G. (1977), Analysis of Housing Data Collected in a Lead-Based Paint Survey in Pittsburgh, Pennsylvania,

Parts I and II (NBSIR 77-1250 and 77-1293), U.S. Department of Commerce, National Bureau of Standards.

5

Arizona Department of Health Services, Division of Environmental Health, Bureau of Sanitation (1976), "Lead-Based Paint: Report of Findings

to the State Legislature" (mimeo).
1-2

The fourth survey was part of a national survey conducted in 1984-1985 to address modernization

needs of public housing. Two hundred and sixty-two public housing units (apartments) plus associated

common areas (i.e., hallways, playgrounds) were inspected in 131 public housing projects in 34 cities.6

Limitations of Previous Surveys

As a basis for national estimates of the number of housing units with lead-based paint, analyzing

other lead hazards in housing, and estimating the cost of abatement, these prior surveys are limited.

Sample Limitation. Because of the limited geographic coverage of most of the surveys, there is

no way of knowing the extent to which the findings are representative of housing in the nation.

Wide Divergence in Estimates of Homes with Lead. The four prior surveys' estimates for the

percentage of homes with lead varied immensely. For housing built prior to 1940, the estimates ranged

from 71 to 100 percent; for homes built between 1940 and 1959, the range was 64 to 92 percent; and for

units built between 1960 and 1977, the range was 48 to 76 percent.

Measurement Imprecision. The portable X-ray fluorescence (XRF) analyzers used to measure

the lead content of paint in all of the surveys have subsequently been found by NIST to be highly

imprecise at the 1.0 mg/cm2 (milligrams of lead per square centimeter of painted surfaces) level7

, which is

the Federal threshold for lead-based paint.

Lack of Dust and Soil Lead Data. The prior surveys provide no information on the prevalence of

lead in house dust and exterior soil--two sources identified in the literature as important pathways of lead.

Therefore, they cannot be used to analyze the prevalence of lead in dust and soil, or the association

between lead-based paint and lead in dust and soil.

Studies of Lead in Surface Dust and Soil

A large number of studies published during the past two decades have indicated an association

between lead dust and childhood blood lead. Three studies established the apparent importance of lead

dust as a pathway for lead-based paint. In 1980, Charney and colleagues concluded that, although several

factors accounted for childhood lead poisoning, lead dust and "hand" lead (i.e., lead that clings to fingers

and hands) were strongly correlated with blood lead, and that interior lead dust should be taken into

account in attempting to reduce lead hazards in residential environments.8

In 1983, based on a HUD-funded study in Baltimore, Charney and colleagues analyzed whether

dust control measures, in addition to treatment of potential lead-based paint hazards, would lower blood

levels. They concluded "that a focused dust-control program can reduce blood lead levels more than

standard lead removal in the home."9

 

6

Wallace, James E. (1986), The Cost of Lead-Based Paint Abatement in Public Housing, U.S. Department of Housing and Urban Development.

7

McKnight, Mary E.; Byrd, Eric W.; Roberts, Willard E.; and Lagergren, Eric S. (December 1989), Methods for Measuring Lead Concentrations

in Paint Films (NISTIR 89-4209), U.S. Department of Commerce, National Institute of Standards and Technology.

8

Charney, E.; Sayre, J.; and Coulter, M. (February 1980), "Increased Lead Absorption in Inner City Children: Where Does the Lead Come

From?", Pediatrics, 65(2).

9

Charney, E.; Kessler, B; Farfel, M.; and Jackson, D. (1983), "Childhood Lead Poisoning: A Controlled Trial of the Effect of Dust-Control

Measures on Blood Lead Levels," New England Journal of Medicine 309(18):1089-1093.
1-3

Bellinger and colleagues (1986) enrolled 249 metropolitan Boston children with low-to-moderate

blood lead levels at one month of age and collected a wide range of data semiannually. Environmental

lead and mouthing behavior were significantly associated with blood lead, but home environment/care

giving, child development, and sociodemographic characteristics were not. Dust lead was the most

important environmental variable, although refinishing and month of sample selection were significant.10

Studies of Pathways Between Paint Lead and Blood Lead

Bornschein, et al. (1986)11 studied the relationship between children's blood lead levels and

measures of the extent of lead-based paint in dwelling units. They found that lead in paint does not

directly impact blood lead levels, but it does impact them through the pathways:

• Lead-based paint hazard ---> dust lead ---> blood lead, and

• Lead-based paint hazard ---> dust lead ---> hand lead ---> blood lead.

The conclusion is that, except for children with pica, an abnormal craving to eat non-food

substances, dust is the major immediate source of lead for children, and that lead-based paint is a primary

contributor to dust lead.

1.2 Report Organization

In the sections that follow, this document presents the design, methodology, findings and

conclusions of the survey, and discusses quality assurance and sources of error in the survey data. The

presentation begins with discussions of the national estimates of prevalence, amounts, and hazards of lead

in paint, dust, and soil in private and public housing. Next, a discussion of research design addresses

sample design, data collection protocols, and quality assurance. Finally, this report addresses the major

conclusions to be drawn from the national survey and its findings.

1.3 Objectives of National Survey of Lead-Based Paint in Housing

The objectives of the national survey were based on Section 302 of the Lead-Based Paint Poison

Prevention Act of 1971, as amended. The informational requirements set forth in that Act are:

• An estimate of the amount, characteristics, and regional distribution of housing in the United

States that contains lead-based paint hazards at differing levels of contamination.

• A comprehensive and workable plan for the cost-effective inspection and abatement of

public housing..., including an estimate of the total cost of abatement.12

 

10Bellinger, D.; Leviton, A.; Rabinowitz, M.; Needleman, H.; and Waternaux, C. (1986), "Correlates of Low-Level Lead Exposure in Urban

Children at 2 Years of Age," Pediatrics 77(6):826-833.

11Bornschein, R.L; Hammond, P.D.; Dietrich, K.N.; Succop, P.A.; Krafft, K.M,; Clark, C.S.; Pearson, D,; and Que Hee, S.S. (1985), "The

Cincinnati Prospective Study of Low-Level Lead Exposure and Its Effect on Child Development Protocol and Status Report," Environmental

Research 38: 4-18.

12Estimates of the costs of abatement are reported in the U.S. Department of Housing and Urban Development reports: Comprehensive and

Workable Plan for the Abatement of Lead-Based Paint in Privately Owned Housing: Report to Congress (1990) and Comprehensive and

Workable Plan for the Abatement of Lead-Based Paint in Public Housing (forthcoming). They are not included in this report.
1-4

• A comprehensive and workable plan, including any recommendations for changes in

legislation, for the prompt and cost-effective inspection and abatement of privately-owned

single family and multi-family housing, including housing assisted under Section 8 of the

U.S. Housing Act of 1937.

Toward these objectives, the National Survey of Lead-Based Paint in Housing was designed to

obtain data for estimating:

• The number of dwelling units in the United States with interior and exterior lead-based

paint, by year built, type of housing, level of lead loading, and census region (see Section

1.4 for an explanation of lead loading).

• The number of multi-family (private and public) residences with lead-based paint in

common areas, by year built, level of lead loading, and census region.

• The extent of surface area of lead-based paint in order to estimate national abatement costs

in public and privately owned housing.

• The prevalence of damaged lead-based paint.

• The prevalence of lead in dust in dwelling units and in soil around the perimeter of

residential structures.

• The characteristics of housing with varying levels of hazard to examine possible priorities

for abatement.

The information was needed to support a number of research questions. These included: analysis

of the relationship among sources and pathways of lead in the residential environment; analysis of the

characteristics of housing with varying hazard levels; development of indices of lead hazard; analysis of

the costs, effectiveness and benefits of alternative strategies of reducing lead-based paint hazards: and the

identification of the dimensions of each of these issues.

1.4 Lead Standards and Guidelines

The Federal Government has set standards and guidelines for lead hazards in paint, dust and soil.

They are briefly discussed here.

The amount of lead in the paint, expressed as the paint lead loading on a surface, is an important

factor in determining the potential exposure level of hazard. For this study, the Federal standard (set by

HUD) is 1.0 milligrams of lead per square centimeter of painted surface (1.0 mg/cm2), and is used to

classify a painted surface as "with" or "without" lead-based paint. Therefore, painted surfaces with 0.9

mg/cm2 of lead are classified as having no detectable lead; and painted surfaces measured at 1.0 mg/cm2

are considered to have lead. At the same time, painted surfaces with lead as high as or in excess of 5.0

mg/cm2 (more common in older homes) are classified in the same way--as having lead-based paint. It

should also be noted that the Federal standard for paint lead loading is not a health-based standard,

implying 1.0 mg/cm2 is not necessarily a threshold for determining safe or unsafe conditions. EPA, along

with other Federal agencies, is currently developing a health-based standard for paint lead, along with

standardized measurement techniques.

Dust lead levels presented in this report are a "loading" and soil lead levels are a "concentration".

Dust loadings refer to the mass of lead per square area of surface, expressed as micrograms of lead per
1-5

square foot of surface (μg/ft2). The HUD Guidelines state that no more than 200 μg/ft2 on floors, 500

μg/ft2 on windowsills and 800 μg/ft2 on window wells is allowed inside a home after lead paint abatement

takes place. (Windowsills are defined by HUD as the lower part of a window inside the room, and

window wells are the bottom of a window between the glass and screen.)

For dust, the guidelines are set by HUD, and were developed for clearance purposes only, i.e.,

declaring an abated residence ready for re-occupancy after lead paint abatement. They were not

developed for determining the presence or absence of health hazards. In addition, readers should be

cautious when comparing the national survey dust lead results to the HUD guidelines because dust

samples in the survey were collected with a vacuum sampling technique and the HUD guidelines were

developed for a wipe sampling technique. The comparability between the two techniques is unknown,

i.e., each technique may give very different results when samples are collected side-by-side. There is

evidence that wipe samples tend to result in higher lead loading then vacuum samples.

Soil concentration is reported as the mass of lead per unit mass of soil, usually expressed as

micrograms of lead per gram of soil (μg/g), or the equivalent parts per million (ppm). The guidelines for

soil lead used in this report (500 ppm) were derived from the EPA's Interim Guidance on Establishing

Soil Lead Cleanup Levels at Superfund Sites and do not necessarily reflect the potential exposures to

occupants near residential structures.

Although the paint, dust, and soil guidelines are not health-based, they do provide a framework to

compare the relative differences among differing characteristics between homes, such as whether leadbased paint is intact or non-intact. As noted for paint lead standards, EPA is currently developing healthbased lead standards for dust and soil.
2-1

2. NATIONAL ESTIMATES OF PREVALENCE

This chapter presents findings on the lead hazard in homes. Some of the estimates are revised from

the estimates reported in the Comprehensive and Workable Plan for the Abatement of Lead-Based Paint

in Privately Owned Housing: Report to Congress (CWP Report) in light of the measurement error

analyses reported in Appendix II, Chapter 3.

2.1 Major Findings and Discussion

An estimated 64 million (77 million to 81 million)13 or 83 percent (± 9%) of private housing units

in the United States built before 1980 have lead-based paint on either interior painted surfaces, exterior

painted surfaces, or both, (57 million (± 5 million), or 74 percent (± 6%) was reported in the CWP

Report). Approximately 782,000 (± 77,000) or 86 percent (± 8%) of pre-1980 public housing units also

have lead-based paint on their surfaces. Although these numbers are vast, they do not necessarily suggest

that each home is an immediate hazard to its occupants. There are many potential factors which determine

the hazards posed by lead-based paint. Several are discussed below.

In addition to the lead loading levels, the condition of the paint is also a factor in determining the

hazards from lead-based paint. Except during renovations, intact lead-based paint probably poses little

immediate risks to occupants; however, peeling, chipping, or otherwise deteriorating paint (non-intact)

may present an immediate danger to occupants. An estimated 14 million or 19 percent of pre-1980

private housing units have non-intact lead-based paint on their surfaces. This is significant not only

because peeling and chipping paint may be directly ingested by children, but it is more likely to break-off

and contaminate house dust and soil. Young children ingest large amounts of dust and soil every day

through normal hand-to-mouth contact. Because of this normal activity, dust and soil are considered to be

the most significant routes of lead exposure to children. Therefore, understanding lead pathways resulting

in exposure is essential to preventing childhood lead poisoning, and was a major goal of this study.

The national survey also examined lead in house dust and in soil next to residential structures.

Thirteen million or 17 percent of private housing units have interior dust lead levels above Federal

guidelines. Similarly, 16 million, or 21 percent, of private housing units have soil lead levels above

guidelines.

National public housing estimates for non-intact lead-based paint were not calculated from the

national survey data because less than 10 homes in the survey had non-intact paint. Dust and soil lead

data also are not presented for public housing because of situations encountered during the field

operations; the dust lead data is suspect because a large number of vacant apartments were inspected.

About 70 percent of the units sampled did not have exposed soil nearby to collect samples -- they were

surrounded by pavement. With sample sizes this small, it was not possible to project national estimates.

The following sections summarize the national survey findings. Section 2.2 discusses private

housing and Section 2.3 covers public housing. For a more complete and technical treatment of the

results, readers are referred to Appendix II, Chapter 2 of this report.

 

13The numbers in parentheses are 95% confidence intervals. See Appendix II, Section 3.4.3 for the methodology used to

compute with the confidence intervals.
2-2

2.2 Lead Paint Hazard in Private Housing

Table 2-1 summarizes data collected and analyzed for the national survey. Among several

characteristics, the data suggests that older homes are more likely to have lead-based paint than newer

homes. An estimated 76 percent (± 12%) of the housing units built between 1960 and 1979 have leadcontaminated paint on their surfaces, but the percentage increases to 90 percent (± 8%) for homes built

before 1960. Also, 12 million (± 1 million) of the homes determined to have lead-based paint are

occupied by families with children under the age of seven. This is an important statistic because

childhood lead poisoning is thought to be the most common and preventable public health concern in our

country today.14

Figure 2-1 shows the prevalence of lead-based paint by location in private housing. In the figure,

the entire circle (pie chart) represents all privately-owned houses in the United States built before 1980

(about 77 million from Table 2-1). An estimated 17 percent of these have no lead-based paint at all (the

white "none" area in the pie chart), while the remainder, or 83 percent of the total, have lead-based paint

somewhere on the building. As is evident from the figure, most houses with lead-based paint have it on

both the interior and the exterior surfaces (53 percent).

It is evident from Figure 2-2 that older homes have considerably more dust and soil lead than

newer homes. The percentage of homes over the guidelines increases from less than 10 percent for post1960 homes to about 50 percent for pre-1940 homes. House dust characteristics are further described in

Figure 2-3. Loadings below and above HUD's guidelines are presented by a bar graph in relation to the

location of lead-based paint and whether it is intact or non-intact. It is important to note that the graph

compares two pieces of information: the estimated number of houses containing lead-based paint relative

to the total number of housing units projected, and the comparison between houses with dust lead within

and exceeding guidelines (the clear bar vs. the black bar). As the bar graph shows, units with intact leadbased paint are less likely to exceed dust lead guidelines than units with non-intact lead-based paint. In

fact, more than half of the homes with non-intact exterior lead-based paint are estimated to have dust lead

loadings above HUD's Guidelines.

Figure 2-4 shows the same type of information for soil as Figure 2-3 presented for dust. Again,

one half of the private housing units in the United States with non-intact exterior lead-based paint have

soil lead concentrations above 500 ppm.

Figures 2-5 and 2-6 are pie charts that show the amounts of lead-based paint on interior and

exterior private housing surfaces for different types of painted architectural components. An estimated 29

billion square feet or 12 percent of all painted interior surfaces are covered with lead-based paint and an

estimated 49 billion square feet or 44 percent of all painted exterior surfaces are covered with lead-based

paint. On average, each private housing unit with lead-based paint has approximately 601 square feet of

the lead paint on the interior and 869 square feet on the exterior. As is evident from the figures, most of

the interior paint is on the walls, ceilings, or floors.

The amounts of lead-based paint in private housing units are further displayed in Figure 2-7. The

bar graph shows that older homes are covered with more square feet of lead-based paint than newer

homes. Figure 2-8 is similar to Figure 2-7, however, it shows the average amount of lead per square

centimeter of painted surface (more precisely, geometric mean paint lead loadings [mg/cm2]) on houses

with lead-based paint. The bar graph clearly displays older homes with more lead contamination in their

paint.

 

14CDC [1991]. Preventing Lead Poisoning in Young Children. U.S. Department of Health and Human Services, Public Health

Service, Center for Disease Control.
TABLE 2-1

ESTIMATED NUMBER OF PRIVATELY OWNED OCCUPIED HOUSING UNITS 

BUILT BEFORE 1980 WITH LEAD-BASED PAINT, BY SELECTED CHARACTERISTICS

(Paint Lead Concentration >= 1.0 mg/sq cm)

Housing Units 

Total With Lead-Based Paint Number of

Occupied Housing Somewhere in Building Housing Units

Characteristic Units (000) (1) Percent Number (000) in Sample (2)

Total Occupied Housing 77,177 83% 64,443 284

 Units Built Before 1980 100% (9%) (6,946)

Construction Year:

1960-1979 35,681 76% 27,275 120

46% (12%) (4,282)

1940-1959 20,476 92% 18,742 87

27% (8%) (1,638)

Before 1940 21,018 88% 18,424 77

27% (9%) (1,892)

Housing Type

Single Family 66,418 85% 56,130 227

86% (9%) (5,978)

Multifamily 10,759 77% 8,308 57

14% (17%) (1,829)

One or More Children 13,912 89% 12,425 90

Under Age 7 18% (9%) (1,252)

Census Region

Northeast 16,963 86% 14,605 53

22% (13%) (2,205)

Midwest 19,848 91% 18,115 69

26% (10%) (1,985)

South 24,967 82% 20,393 116

32% (10%) (2,497)

West 15,399 73% 11,298 46

20% (18%) (2,772)

Owner-Occupied (2) 50,554 84% 42,516 179

(9%) (4,550)

 Market Value of Home

Less than $40,000 11,885 92% 10,888 39

24% (12%) (1,426)

$40,000 to $79,999 19,401 90% 17,550 46

38% (10%) (1,976)

$80,000 to $149,999 11,863 68% 8,093 45

23% (18%) (2,135)

$150,000 and up 7,405 85% 6,276 42

15% (15%) (1,111)

Renter-Occupied (2) 24,734 82% 20,329 105

(11%) (2,721)

 Monthly Rent Payment

Less than $400 16,339 85% 13,811 59

66% (14%) (2,287)

$400 and up 8,395 81% 6,822 40

34% (15%) (1,259)

Household Income (2)

Less than $30,000 46,126 85% 39,032 156

60% (10%) (4,613)

$30,000 and up 31,048 81% 25,121 127

40% (11%) (3,415)

 (1) Total units data are from the 1987 American Housing Survey.

 (2) Some respondents did not respond to the questions on economic variables. Therefore, counts for disaggregation 

 may not add to corresponding aggregate counts.

 Note: Numbers in parentheses are approximate half-widths of 95% confidence intervals for the estimated percents and

 numbers. For example, the approximate 95% confidence interval for the percent of housing units with some

 lead-based paint is 83% + / -9% or 74% to 92%.
 2-4

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Figure 2-1 

Prevalence of Lead-Based Paint by Location in Privately Owned Occupied

Housing Units

Interior Only

10%

Both Interior and

Exterior

53%

None

17%

Exterior Only

20%

See Appendix II, Table A-1 for underlying data
Before 1940

1940-1959

1960-1979 Construction Year

Dust Lead Exceeding

Guidelines

Soil Lead Exceeding

Guidelines

0%

10%

20%

30%

40%

50%

60%

Percent 

Housing 

Units

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Figure 2-2

Estimated Percent of Privately Owned Housing Units with Dust and Soil Lead

Exceeding Guidelines by Construction Year

(2) Soil lead guideline levels are 500 ppm. 

500 ug/sq. ft. on window sills and 800 ug/sq. ft. in window wells

(3) See Appendix II, Table 2-25, and Table 2-27 for underlying data

(1) Surface dust lead guidelines are 200 ug/sq. ft. on floors,
No LBPInterior

Intact

LBP

Interior

Non

Intact

Exterior

Intact

LBP

Exterior

Non

Intact

Condition of Paint

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000

Number of 

Housing Units

(000)

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Figure 2-3

Number of Privately Owned Housing Units with Interior Dust Lead Levels Above

Guidelines by Presence and Condition of Lead-Based Paint (LBP) 

Dust within guidelines

AAAA

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Dust exceeding guidelines

(1) "Within Guidelines" means that surface dust lead does not exceed 200 ug/sq. ft. on floors, 500

ug/sq. ft. on window sills, and 800 ug/sq. ft. in window wells. See HUD Interim Guidelines

(2) A housing unit has non-intact interior LBP if there are more than 5 sq. ft. of damaged interior LBP.

(3) See Appendix II, Table 2-6 for underlying data
No

Exterior

LBP

Exterior

Intact

LBP

Exterior

NonIntact

Presence and Conditon of Exterior

Lead-Based Paint

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

Number of Housing

Units (000)

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Figure 2-4

Number of Privately Owned Housing Units with Lead in Soil by Presence and

Condition of Exterior Lead-Based Paint

Soil Lead Within Guidelines

AAA

AAA

AAA

Soil Lead Exceeding Guidlines

(1) "Within Guidelines" means soil lead is less than 500ppm

(2) A housing unit has non intact exterior lead based paint if there are more than 5 sq. ft. of damaged exterior LBP.

(3) See Appendix II, Table 2-7 for underlying data
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Figure 2-5

Average Amount of Lead-Based Paint (LBP) Per Housing Unit on Interior

Surfaces by Painted Component for Privately Owned Housing Units

(LBP) Concentration > = 1.0 mg/sq cm)

Non-Metal

Components 

146 sq. ft.

Metal Components 

2 sq. ft.

Shelves/Other 

82 sq. ft.

Walls/Ceiling/Floor

371 sq. ft.

Total of 601 square feet per housing

See Appendix II, Table 2-9 for underlying data
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Figure 2-6

Average Amount of Lead-Based Paint (LBP) Per Privately Owned Housing

Unit on Exterior Surfaces by Painted Component 

(LBP concentrations >= 1.0 mg/sq cm)

Walls, 681 sq. ft.

Metal Components

7 sq. ft.

Non Metal

Components

169 sq. ft

Porches/ Other, 13

sq. ft.

Total of 870 square feet per housin

See Appendix II, Table 2-10 for underlying data
2-9

2.3 Lead Paint Hazard in Public Housing

Table 2-2 shows that an estimated 782,000 units, or 86 percent of the pre-1980 housing stock have

lead-based paint somewhere in the unit. As with private housing, older public housing units are more likely

than newer ones to have lead-based paint. In fact, nearly all (97 percent) of pre-1950 public housing has

some lead-based paint.

Figure 2-9 shows the distribution of lead-based paint on public housing units. The data shows that

interiors have more lead-based paint than exteriors. This is the opposite of the private housing results,

where more lead-based paint was estimated to be on the exteriors of dwellings.

While most of the interior lead-based paint in public housing (like private housing) is on the walls,

ceilings or floors (Figure 2-10), exteriors in public housing show a different trend. Figure 2-11 shows that

most of the paint on public housing exteriors is on non-metal components, including such items as trim,

window molding, doors, soffit, and fascia, (not exterior walls). This finding may reflect a majority of

public housing units with unpainted brick or concrete exterior walls.

Figure 2-12 for public housing parallels Figures 2-8 for private housing. Figure 2-12 shows that

age contributes to the amount of lead on the painted surfaces, similar to Private housing. Geometric mean

paint lead loading levels are higher for the pre-1950 dwelling units.
TABLE 2-2

ESTIMATED NUMBER AND PERCENT OF PUBLIC HOUSING UNITS 

BUILT BEFORE 1980 WITH LEAD-BASED PAINT, BY SELECTED CHARACTERISTICS

 (Paint Lead Concentration >= 1.0 mg/sq cm)

Housing Units

Total With Lead-Based Paint Number of

Public Housing Somewhere in Building Housing Units

Characteristic Units (000) Percent Number (000) in Sample

Total Public Housing Units Built 910 86% 782 97

Before 1980 100% ( 78% - 94% ) ( 705 - 858 )

Construction Year: 1960-1979 455 79% 359 43

50% ( 66% - 92% ) ( 299 - 419 )

1950-1959 273 90% 246 24

30% ( 77% - 100% ) ( 209 - 273 )

Before 1950 182 97% 177 30

20% ( 88% - 100% ) ( 160 - 182 )

 Notes: (1) Numbers in parentheses are 95% confidence intervals for the estimated percents and numbers.

 (2) Categories with small sample sizes should be interpreted with caution.

 2-10
Before 1940

1940 - 1959

Construction Year 1960 - 1979

Interior Paint

Exterior Paint

0

200

400

600

800

1000

1200

1400

1600

Sq. ft. of LBP per

Dwelling Unit

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Figure 2-7

Amounts of Lead-Based Paint by Location and Construction Year for Privately

Owned Housing Units

(LBP Concentration >= 1.0)

See Appendix II, Table A-6 & A-7 for underlying data
Before 1940

1940 - 1959

Construction Year 1960 - 1979

Interior Paint

Exterior Paint

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

Mean Loadings in

mg/ sq. cm

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Figure 2-8

Geometric Mean Paint Lead Loadings in Privately Owned Housing Units by

Location and Construction Year

(LBP Concentration >= 1.0 mg/ sq.cm)

See Appendix II, Table A-8 for underlying data
 2-12

Unit

Interior

Interior

Common

Areas

Building

Exteriors

Somewhere

in 

Building

Location 

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

Percent 

Housing

Units

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Figure 2-9

Percent of Public Housing Units with Lead-Based Paint (LBP) by Location

(LBP Concentration >= 1.0 mg/ sq. cm)

See Appendix II, Table 2-30 for underlying data
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Figure 2-10

Average Amounts of Lead-Based Paint (LBP) per Public Housing Unit on

Interior Surfaces by Architectural Component

(LBP Concentration >= 1.0 mg/sq cm)

Wall/ Ceiling/ Floor 282 sq. ft.

Metal Components

32 sq. ft.

Non-Metal Components

47 sq. ft.

Shelves/ Other 6 sq. ft.

Total of 367 square feet per unit, average, interior

See Appendix II, Table 2-31 for underlying data
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Figure 2-11

Average Amount of Lead-Based Paint (LBP) in Publicly Owned Housing Units

on Exterior Surfaces by Architectural Component 

(LBP concentrations >= 1.0 mg/sq. cm)

Walls, 13 sq. ft.

Metal Component

45 sq. ft. Non-Metal Component 

71 sq. ft.

Porches/Other, 4 sq. ft.

Total of 133 square feet per unit, average, exterior See Appendix II, Table 2-32 for underlying data
 2-14

Before 1950

1950 - 1959

Construction Year 1960 - 1979

Interior Paint

Exterior Paint

0

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1

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Mean Loadings in

mg/ sq. cm

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Figure 2-12

Geometric Mean Paint Lead Loadings in Publicly Owned Housing Units by

Location and Construction Year

(LBP Concentration >= 1.0 mg/ sq.cm)

See Appendix II, Table B-4 for underlying data
3-1

3. RESEARCH DESIGN

This chapter presents a brief description of the research design for the national survey of lead-based

paint in housing. A complete technical discussion can be found in Appendix I of this report. The study

population consisted of nearly all housing in the United States constructed before 1980. Newer houses

were presumed to be no detectable lead because, in 1978, the Consumer Product Safety Commission

banned the sale of lead-based paint to consumers and the use of such paint in residences. Group quarters

(e.g., dormitories and jails) and projects that are occupied exclusively by the elderly were excluded from the

survey, because the primary public health concern was lead poisoning in children. Also excluded for

operational reasons were vacation homes, homes in Alaska and Hawaii, and military housing.

The broad elements of the design included:

• A national area probability multi-stage sample survey of lead-based paint in homes, to permit

statistically valid estimates of the parameters required for the development of federal policy.

• In-person visits to the sampled homes to identify, describe, and measure painted surfaces and

to measure the lead content of the paint.

• Collection and laboratory analysis of dust and soil samples in and around each sampled

home, to permit the statistical analysis of the associations among lead in paint, dust and soil.

3.1 Sample Design

This section presents the sample design of the national survey. Private and public housing were

sampled, using somewhat different methodologies. This section covers both.

In order to optimize the Congressionally required estimates (see Chapter 1), a design stratified on

dwelling unit age and type was constructed. Dwelling units were grouped into three types of housing --

privately-owned single family, multifamily, and public housing -- and three age categories. Table 3-1

displays the national distribution of pre-1980 dwelling units. The survey was conducted between

December 1989 and March 1990. The final sample contained 284 privately-owned dwelling units and 97

public housing units, for a total sample size of 381 dwelling units. Table 3-2 displays the distribution of

the final sample across the strata.

The sample design was the result of compromise between funding availability and the research

objectives. The sample was affordable and provided the statistical accuracy needed to develop national

estimates upon which government policy could be based. It provided estimates that were sufficiently

precise for the comprehensive and workable plans for private and public housing. For example, 95 percent

confidence intervals for estimates of the incidence of lead-based paint in private housing in any of the three

periods of construction used in Table 3-1 were within plus or minus 10 percent.

The multi-stage design outlined below was chosen over other approaches because it efficiently and

economically satisfied the major operational requirements of the study. The objectives and design of the

study required in-person visits to the sampled dwelling units. The geographic clustering of homes allowed

those visits to be conducted much more economically. Also, a survey sample requires a sampling frame,

i.e., a list of all dwelling units eligible for the survey. For private housing, no such list exists nationally, or

even in many localities. In light of time and cost constraints, the required number of lists was minimized
Table 3-1

National Distribution of Dwelling Units Built Before 1980

Number of Pre-1980 Dwelling Units (000)

Construction Year

Type 1960-1979 1940-1959 pre-1940 Total

Privately Owned- Occupied

 Single Family 29,137 18,782 18,499 66,418

 Multifamily 6,548 1,690 2,521 10,759

Sub-Total 35,685 20,472 21,020 77,177

1960-1979 1950-1959 pre-1950 Total

All Public, Family Units 182 278 346 807

Total 35,867 20,750 21,366 77,984

 Source: 1987 American Housing Survey.

Table 3-2

Distribution of Completed Inspections

By Construction Year and Dwelling Unit Type

Completed Inspection Visits

Construction Year

Type 1960-1979 1940-1959 pre-1940 Total

Privately Owned- Occupied

 Single Family 94 72 61 227

 Multifamily 26 15 16 57

Sub-Total 120 87 77 284

1960-1979 1950-1959 pre-1950 Total

All Public, Family Units 30 24 43 97

Total 150 111 120 381

 3-2
3-3

by using the multi-stage area probability sample for the private housing. A geographic clustering of the

sampled homes was deemed to be operationally efficient and statistically acceptable. Also, tying the

development of the public housing list frame to the same localities as used for the private housing extended

the efficiency of the clustering of the whole survey operation.

The first stage of the sample selection consisted of selecting 30 counties -- stratified by region and

climate, and selected with probability proportional to the 1980 population -- from approximately 3,000

counties in the United States. A survey sample requires a sampling frame, that is, a list of all dwelling

units eligible for the survey. Although no such list exists for private housing, HUD maintains a list of

public housing projects suitable for use as a frame. Thus, private and public housing were sampled using

different within-county designs. The different ownership structures between public and private housing

also required different approaches for the owners and occupants. These two approaches are summarized

below.

Privately Owned Housing. A multistage area probability design was developed and employed to

sample private housing and approach the occupants. A description of the design and its within-county

implementation follows.

• Five census blocks were statistically selected in each of the 30 counties. To ensure that the

full spectrum of income levels would be represented in the sample, a measure of wealth was

computed for each census block. One census block was selected from each one-fifth of the

range of this wealth measure.

• Field interviewers were sent to each of the 150 census blocks to list every dwelling unit. This

process created a frame for the sampling of dwelling units. The interviewers listed 27,833

dwelling units, an average of 186 per census block.

• Samples of dwelling units were selected from the lists. A brief in-person screening interview

was conducted with an adult occupant in each sampled dwelling unit to determine if the unit

was eligible for the survey and, if so, which of the six age/type strata in Table 3-1 it belonged

to.

• A sample of dwelling units was randomly selected from the eligible homes according to the

survey design in a manner that ensured that all eligible segments were represented in the

sample.

• Telephone calls were made to the sampled homes to collect basic information about the

dwelling unit and the occupants and to schedule an appointment to visit the dwelling unit. An

incentive of $50 was paid to each respondent who permitted a completed inspection.

Public Housing. The public housing sample was designed in a somewhat different manner than the

private housing sample. All projects in the 30 sampled counties were extracted from the public housing

data tape supplied by HUD. The cognizant public housing authorities (PHAs) were contacted and asked to

verify and/or correct the frame data (primarily address and number of family units) for their projects. A

substantial number of additions, deletions and modifications were made to the 30-county public housing

frame. Projects were then sampled with probability proportional to the number of family units, and

according to the construction year strata in Table 3-2. Finally, individual housing units within projects

were selected with equal probability. It was necessary to work through the chain-of-command to contact

the sampled projects and make appointments to inspect sampled units. The chain of command typically

included the HUD regional office, the PHA headquarters, and the project manager. Public housing tenants

who consented to the inspection received the same $50 incentive as private housing occupants.
3-4

3.2 Inspection Protocol

Resource limitations did not permit the complete identification, inspection, quantification, and

testing of every painted surface in every inspected dwelling unit. Fortunately, the objectives of the study

did not require such thorough inspections. It is possible in survey statistics to develop a good, clear picture

of the aggregate population with only limited information on each sampled individual. Consequently, the

limited inspection protocol described below was followed in each dwelling unit. The inspection protocol

was the same for both public and private housing units.

The inspection visits were performed by a two-person team: a field interviewer who interviewed the

occupant and collected and recorded the information; and a technician who performed x-ray fluorescence

(XRF) testing of the lead content of the paint and collected the dust and soil samples.

Interior Rooms. The rooms were inventoried and classified into wet and dry rooms according to

the presence or absence of plumbing in the room. One wet room and one dry room were randomly selected.

All painted surfaces in each of these two rooms were identified and quantified; the substrate materials were

identified; the condition of the paint and substrate materials were noted. Painted surfaces were grouped

into four strata of architectural components: walls, ceiling, and floors; trim on metal substrates (molding,

window frames, door frames, etc.); trim on nonmetal substrates; and other (built-in shelves, cabinets, etc.)

Five surfaces in each room were randomly selected to be tested for lead content. One surface was selected

from each of the four strata, with a fifth randomly selected from all four strata. The paint lead

measurements were made with Scitec MAP-3 spectrum analyzer X-ray fluorescence devices (MAP/XRFs).

Samples of dust were collected by vacuuming in three locations in each sampled room: the floor, a

window sill, and a window well. In addition, a dust sample was collected from the floor near the most-used

entrance to the building. The floor is a collection sink for dust and children come into direct contact with it

when crawling or playing. The windows are boundaries between the interior of the unit and exterior

sources of environmental lead. Because the abrasion of opening and closing windows causes paint dust to

collect on horizontal window components, the wells are collection sinks for dust. Entry ways and common

heavy traffic areas are more likely to collect deposits of soil tracked in from outside the building. The dust

samples were sent directly to a laboratory to be analyzed for their lead content.

Exterior. An exterior wall was randomly selected for inspection. All painted surfaces on the

sampled wall were cataloged in the same manner as the interior rooms and subjected to XRF testing. Three

exterior soil samples were collected: at the drip line along the sampled wall, at a remote location away

from the building, and at the most-used entrance to the dwelling unit. The entry way is a proximate source

of exterior soil lead that could be tracked into the interior. The drip line of a wall is the collection point for

run-off from painted exterior wall; flaking paint or paint components leached by rainwater can collect in

the soil. The remote location provided data on the background contribution of environmental sources of

lead not associated with the unit or building itself. The soil samples were also sent to a laboratory for

lead content analysis.

Because random techniques were used to sample painted surfaces, there was concern that some leadbased paint in the home might go undetected. To minimize the probability of missing lead-based paint in a

home, technicians looked for and tested any painted surface in the dwelling unit deemed likely to contain

lead. If the first test failed to find lead, a second surface was tested. Due to practical constraints, the

technicians sometimes were limited to searching for lead-based paint in areas of the dwelling unit entered

during the course of the inspection and did not wander throughout the dwelling unit looking for lead-based

paint. A similar set of one or two purposive samples was taken for the exterior wall.
3-5

Common Areas. Common areas were inspected in multifamily residences. If an interior common

hall existed, two dust samples were taken: one sample was taken from just outside the dwelling unit and

one just inside the main entrance to the building. If the building had common rooms such as a mail room,

laundry room, community room, etc., one was randomly selected and was inspected according to the

protocol used for the wet and dry rooms. Finally, playgrounds were inspected. Each piece of playground

equipment was quantified, described, and tested via XRF. Three soil samples were taken from the

playgrounds.

3.3 Environmental Sampling Protocols

Paint Sampling. The lead-based paint testing was accomplished by MAP/XRF devices that

estimated the lead content of the paint.15 The MAP/XRF was equipped with a full-intensity 40-millicurie

Co57 source. The protocol called for the technician to place the MAP/XRF's scanner against the sampled

component, hold it stationary and flat against the surface throughout a 60-second reading, then record the

reading from the MAP/XRF's console.

Selection of MAP/XRF Equipment. There were two primary rationales for choosing the

MAP/XRF to test for lead in paint. The spectrum analyzer MAP/XRFs were used in preference over

direct-read XRFs because the National Institute of Standards and Technology (NIST) had determined them

to be more accurate and precise than the direct-reading XRFs used in earlier surveys.16,17 The MAP/XRF

was used in preference to taking paint scraping samples because the survey was conducted in occupied

dwellings where it was not feasible to take scrapings for laboratory analysis.

The spectrum analyzer MAP/XRF devices still had limitations. In particular, the MAP/XRF

generally produced readings that were systematically different from the amount of lead in paint being

tested. The direction and magnitude of the differences were related to the substrate material and the lead

loading in the paint. Furthermore, the precision of the readings depended on the substrate. On metallic

substrates, the MAP/XRF's readings were systematically higher than the true lead loadings, for all

observed levels of lead. On concrete, brick, and other related substrates, the MAP/XRF had great

difficulty detecting low to moderate levels of lead in paint, and there was much variation in readings.

Dust Sampling. The dust collection protocol employed a portable vacuum pump fitted with a length

of tubing, a filter cassette, and a collection nozzle inserted over the filter cassette. The protocol specified

laying down a template that outlined an area of one square foot. The technician vacuumed the area in

overlapping passes, first left to right over the entire area and then top and bottom. Care was taken to hold

the nozzle level to the surface and to move the nozzle at a steady rate. Next, the template was moved over

one foot and the process repeated until four square feet were vacuumed. This protocol required about four

minutes. For areas which could not accommodate the template, such as window wells, the entire area was

vacuumed and dimensions of the area were recorded.

 

15Consideration was given to scraping samples of paint for laboratory analysis. Laboratory analysis is more precise and accurate than in situ

MAP/XRF. However, it requires damaging painted surfaces in people's homes. It was felt that the gain measurement precision and accuracy would

be more than offset by effects of a very large refusal rate.

16McKnight, Mary E.; Byrd, W. Eric; and Roberts, Willard E. (May 1990), Measuring Lead Concentrations in Paint Using a Portable Spectrum

Analyzer X-Ray Fluorescence Device (NISTIR W90-650), U.S. Department of Commerce, National Institute of Standards and Technology.

17McKnight, Mary E.; Byrd, W. Eric; and Roberts, Willard E. and Lagergren, Eric S. (December 1989), Methods for Measuring Lead Concentration

in Paint Films (NISTIR 89-4209), U.S. Department of Commerce, National Institute of Standards and Technology.
3-6

Soil Sampling. The soil sampling protocol called for the field technicians to use a soil corer with

plunger to collect soil. The sample plug was expelled from the corer into a plastic bag. For each sampled

location, the technician drew three soil plugs from the ground, the first as close as possible to the targeted

sample site, and the other two twenty inches to either side of the first. The protocol defined the soil sample

for each location as the blended composite of the three soil plugs.

3.4 Quality Assurance

Quality assurance was an integral component of the study design and execution. This section

summarizes the quality assurance procedures employed in the survey.

3.4.1 Measures to Enhance Response Rates

In the national survey, as any survey, maximizing response rates is critical to minimizing bias and

maintaining the representativeness of the data. Maintaining participation at the point of the home

inspections was particularly important because of the investment of effort that was required to reach that

point. For private housing, efforts to ensure participation began with in-person visits to homes for

screening purposes. In addition to the personal contact initiated by the interviewer, a letter from HUD

explaining the survey and verifying its legitimacy was left with the dwelling unit respondent.

After dwelling units were selected from among the eligible dwelling units, telephone calls were

placed to the residents. The interviewers were trained to explain the survey and answer any questions or

concerns the resident might have. At times convenient to the respondents, the telephone interviewer

scheduled appointments for inspections to occur five to ten days after the phone call. Minimizing the delay

between the call and the inspection reduced the opportunity for the respondents to reconsider their

agreement to participate. The residents were informed at the time of this call that they would receive a $50

incentive for allowing the home inspection.

3.4.2 Quality Assurance for MAP/XRF Data

Extensive quality assurance (QA) procedures were developed for use of the MAP/XRF in the

national survey.

Eight "standards" were developed to conduct quality assurance readings. A "standard" consisted of

a small, 3" x 4" plastic sheet (i.e., shim) painted with paint containing a known level of lead and placed

tightly on a piece of background material (called a substrate). NIST manufactured the shims used in the

survey. The substrates of interest were four common dwelling unit building materials: wood, drywall,

steel, and cement. All substrates used in the construction of standards had a smooth surface that allowed

the shim to be tightly and evenly affixed. Two different shims were used. One shim contained 0.6 mg/cm2

of lead, the other 2.99 mg/cm2. The four substrates and two shims were layered in combinations to make

eight test standards.

Baseline Readings. Upon receipt from the manufacturer, a quality assurance technician performed

eight 60-second readings on each of the eight standards. This produced a baseline of 64 readings of

different lead loadings on different substrate materials for each MAP/XRF used in the study. The testing

helped establish that each MAP was ready to be used in the field.
3-7

Close-out Readings. The above procedures were repeated in full when a MAP/XRF was retired

from the field, and before returning it to the manufacturer.

In-Field Readings. In a scaled-down procedure, one reading was taken on each standard for a total

of eight readings every day that the MAP/XRF was in the field and in use. This practice had the additional

benefit of helping detect machine drift and malfunction. Technicians were instructed to call their

supervisor if readings varied from original baseline readings by over 30 percent. The procedure also helped

detect if batteries had become low and needed replacement. The in-field QA readings were not used by the

technicians to adjust the MAP/XRF readings in the field. Rather, the raw MAP/XRF readings were

recorded. During the data analysis, the QA readings were used to develop adjusted MAP/XRF readings.

3.4.3 Field Quality Assurance Measures

Prevention of Contamination of Dwelling Units and Samples. There was concern that the

inspection team might bring lead into the home. To help minimize this problem, each team member put

paper slippers over his or her shoes before entering the unit. Team members wore rubber gloves during the

inspection. The technician discarded the gloves after he took each dust and soil sample, replacing them

with new ones. He replaced the dust sampling vacuum nozzle with a clean one after each sample. The

technician also cleaned the corer after each soil sample.

Quality Assurance for Field Equipment and Supplies. Efforts were taken to ensure that the

equipment or supplies themselves did not introduce lead contamination. Wet wipes used to clean soil

sampling equipment were tested for lead. Shavings from the soil sampling equipment, including the painted

handle, were tested. Particular caution was observed in testing supplies that technicians were expected to

purchase while in the field. Several brands of plastic bags and wet wipes were tested to ensure that

commonly available brands would not introduce any lead contamination.

3.5 Limitations of the Study Design

This research design reflects an explicit boundary of the survey. All audiences of the national

survey results should be aware it was never the survey's objective for the testing of sampled paint surfaces

within homes to be sufficient to prove or disprove if any specific home had a lead hazard, or the potential

for such. The data collection was designed to provide the supporting basis for national estimates, not to

determine definitively whether a particular house had lead-based paint present.

The statistical sample was specifically designed to permit the development of valid national

prevalence estimates, even with limited data on any particular dwelling. Given the ratio of sampled surfaces

to the total number of painted surfaces in a home, it is readily conceivable that lead-based paint could be

present in a given home but not detected as part of a statistically based sampling procedure. Conversely,

the testing protocol could have produced a very high lead reading where there was, in fact, no current

hazard (e.g., lead-based paint was present, but was totally enclosed or covered with epoxy or acrylic).

Extensive lead testing designed to say with certainty whether a lead hazard existed in each unit was

beyond the scope of the survey and would have substantially increased costs and effort levels. The

increased time spent in each unit may have reduced the overall response rate, with a resulting decrease in

the quality of the overall data, rather than the increased quality that might be expected from such increased

effort.
4-1

4. SOURCES OF ERROR IN THE NATIONAL SURVEY DATA

In order to assess the utility of the national survey data for lead research and policy development,

an evaluation of the quality of the data is needed. Data quality is determined by the processes and

procedures that generated the data including sample design and selection, response rates, field and

laboratory measurements.

One primary objective of the national survey was to estimate the nationwide percentage of

dwelling units with lead-based paint. A dwelling unit is classified as having lead-based paint if any

surface within the dwelling unit has an average paint lead concentration greater than 1.0 mg/sq cm. The

determination of whether the average paint lead concentration across a surface was greater than 1.0

mg/sq cm was subject to two sources of error: systematic differences between the MAP/XRF readings

and the actual paint lead concentrations; and misclassifications of surfaces due to random variability in

the MAP/XRF readings. The classification of a dwelling unit as having lead-based paint was subject to

several additional error sources, including: sampling error due to the random sampling of housing units;

systematic differences between the study respondents and non-respondents; sampling error due to the

random selection of rooms and painted components within rooms for the MAP/XRF measurements; and

misclassifications of dwelling units due to the incomplete sampling of rooms. Failure to take these

sources of error into account in the data analysis can produce biased prevalence estimates and

overestimates of the precision in the estimates.

The difference between an MAP/XRF measurement and the actual lead concentration on the

surface being measured is called measurement error. The presence of measurement error does not mean

that the measurement was incorrectly made, but only that there was a non-zero difference (usually

assumed to be random) between the MAP/XRF measurement and the actual concentration. If the average

of the measurement errors is zero then the measurements are said to be unbiased and individual

measurements were sometimes higher and sometimes lower than the actual lead concentrations. If the

average of the measurement errors is other than zero, the measurements are said to be biased.

This chapter presents a brief discussion of these issues. Both sampling issues and MAP/XRF

measurement errors are included. A detailed discussion is presented in Appendix II, Chapter 3.

4.1 Response Rates and Potential for Non-Response Bias

An analysis of response rates was conducted to estimate the potential impact of national survey

nonresponse on the estimated prevalence of lead-based paint in housing. The analysis looked at the

relationship between response rates and factors such as geographic location, ethnicity, and economic

characteristics (e.g., rent, home value, and income) that could potentially influence response rates. In

addition, the analysis studied the association between inspected housing units in the same or nearby

census blocks with respect to the presence or absence of lead in paint, dust, and soil.

4.1.1 Private Housing

Table 4-1 displays contact, response, and eligibility rates at the national level. The eligibility rate

applies only to the screener stage, when in-person interviews were conducted to screen homes for

eligibility in the survey. Contact rates were calculated for both the screener and telephone interview

stages (when respondents were asked to permit an inspection of their home), whereas response rates were

calculated for all stages. The definition of a completed case in Table 4-1 varies with the stage of data

collection. A case was considered completed at the screener stage if an interview was completed, whether

or not the respondent was eligible. The screener response rate thus measures the rate at which a screening
4-2

interview reaches its logical conclusion (eligible or ineligible), and did not terminate due to other causes

(refusals, etc.). At the telephone interview stage, only eligible respondents who completed interviews and

scheduled appointments were considered completes. Finally, a case was considered complete at the

inspection stage if an inspection was completed.

Table 4-1

National Response, Contact, And Eligibility Rates At Each

Data Collection Stage

Data Collection Stage Contact Rate Response Rate Eligibility Rate

Screener 77% 63% 89%

Telephone Interview 83% 55% --

Inspection -- 90% --

Notes:

• The Contact Rate is the number of contacted households divided by the in-scope number attempted.

• The screener Eligibility Rate is the number of eligible cases divided by the number of completed screening

interviews.

• The Response Rate is the number of completed cases divided by the in-scope number completed.

The ethnic and economic distributions of housing units in the national survey were compared to the

corresponding distributions in the 1987 American Housing Survey performed by the Census Bureau and

HUD. No significant differences were formed with respect to ethnicity, building age or family income.

There were a few instances of significant differences: The national survey had fewer very low rent (<

$200 per month) homes than expected, fewer high market value homes (> $150,000) than expected and

more homes in the South than expected. There is a strong positive association between inspected housing

units in the same census block with respect to the presence or absence of lead in paint, dust, and soil.

That is, if one house in a census block has lead-based paint, other houses in the same census block are

also likely to have it. These findings suggest that the potential bias from nonresponding housing units is

likely to be small. Therefore, the estimates of lead-based paint prevalence were not modified to adjust for

non-response.

4.1.2 Public Housing

For the public housing component of the national survey, a sample of 110 projects from a national

frame of public housing projects was drawn according to the design described in Chapter 3. The survey

was completed in 97 of the sampled projects, indicating negligible potential for non-response bias in the

sample of public housing projects.

However, analysis of the sampling of housing units within the public housing projects showed that

there was an apparent over-representation of vacant housing units. The public housing survey design

called for randomly selecting one housing unit from each sampled project. This design was difficult to

implement in the field because a number of the public housing project managers apparently felt it was

more convenient to permit the field team to sample vacant housing units. Consequently, there were 44

vacant public housing units in the sample of 97 units. Although a comparison of the prevalence of lead in

paint between vacant and occupied housing units showed no significant differences, the impact on other

target parameters is unknown. For example, it would be difficult to estimate the percentage of public
4-3

housing units with lead-based paint and children under age seven because so many vacant apartments

made up the sample. Furthermore, dust samples collected in vacant apartments probably do not represent

samples collected in occupied apartments. Because the public housing sample sizes were small and the

occupied housing unit sizes were even smaller, definitive conclusions resulting in national estimates of

dust lead levels are not possible.

4.2 MAP/XRF Measurement Bias

As described in Chapter 3, to assure a continual check of the accuracy and performance of the

MAP/XRF analyzers during the national survey, daily validation measurements were made. Statistical

analyses were performed on the validation data to estimate the precision and accuracy of the MAP/XRF's

readings, and to relate them to the substrate, concentration level, and age of the Co57 source. Equations

were developed to relate the lead concentrations on the substrates to the MAP/XRF readings. A different

equation was developed for each combination of machine and substrate. These equations were inverted to

generate equations to statistically calibrate the MAP/XRF readings.

This analysis of the validation data led to the conclusion that the MAP/XRF devices used in the

National Survey generally produced readings that were systematically different from the actual amount of

lead in the paint. The direction and magnitude of the systematic differences were related to the substrate

material, the lead concentration in the paint, and, to a lesser extent, the age of the Co57 source. The exact

nature of the relationships varied from one individual MAP/XRF to another, sometimes significantly.

Furthermore, the precision of the readings depended on the substrate. Specifically, the MAP/XRF tended

to under-estimate low levels of lead in paint on wood, drywall, and plaster and over-estimate high levels

of lead. Also, the MAP/XRF's readings were systematically greater than the true lead loadings on steel

and other metallic substrates and it had great difficulty detecting low or moderate levels of lead in paint

on concrete, brick, and other related substrates.

Censoring of the MAP/XRF Readings

Although the cause of biased readings can come from several factors, an important factor in this

study is censoring. The MAP/XRF instruments used in the national survey were designed to never report

a reading below zero even though readings below zero were otherwise possible. These MAP/XRF

readings, which would have been below zero but which were recorded as zero, are referred to as censored

MAP/XRF readings and contribute to bias. In the survey, censoring affected primarily the low readings

on concrete substrates. Since this group of readings comprised only a small proportion of all MAP/XRF

readings, the effect of censoring on the national estimates is not significant.

4.3 Classification Error Due to MAP/XRF Measurement Variation

Random variation in the MAP/XRF measurements can lead to incorrect classification of a surface

as having or not having lead-based paint. The MAP/XRF measurement on a surface with paint lead

concentration less than 1.0 mg/sq cm may be greater than 1.0, or vice versa, resulting in a

misclassification. If the number of surfaces which are misclassified as having lead based paint is different

than the number of surfaces misclassified as not having lead based paint, the estimated percentage of

surfaces in a dwelling unit with lead-based paint will be biased. This is called classification bias. Note

that classification biases can exist even when the MAP/XRF measurements are unbiased. Estimates of the

percentage of surfaces within a dwelling unit with lead-based paint can be either low or high by as much

as eight percent. Estimates of the proportion of surfaces nationally which have lead-based paint will

have less than one percent bias.
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4.4 Classification Error Due to Dwelling Unit Sampling Procedures

Within each dwelling unit, MAP/XRF measurements were made on randomly selected surfaces

within one randomly selected wet room and one randomly selected dry room. However, the classification

of a dwelling unit as having lead-based paint depends on the lead concentration on all surfaces within a

dwelling unit. Using only the MAP/XRF measurements on the measured surfaces, a dwelling unit might

be misclassified as not having lead-based paint when it actually did, because the surfaces with lead-based

paint were not among those selected for measurement.

To help accurately predict the prevalence of housing units with lead-based paint and thus, estimate

the misclassification rate, it was necessary to develop a mathematical simulation model based on data

from the survey and other sources. The model was used to statistically remove the classification biases

induced by incomplete sampling of rooms and surfaces within a dwelling unit and by measurement

variation. Extending the results from the measured surfaces to all surfaces in the unit was based on: data

on the number of rooms in the unit; data on the number of surfaces per room; and assumptions about the

relationship of the lead concentrations on unmeasured surfaces to those on the sampled and measured

surfaces. The classification of dwelling units as having or not having lead-based paint can be biased

downward by 10 to 25 percentage points when only a few surfaces within the dwelling unit are measured.

4.5 Impact on the National Estimates of Prevalence

All statistical findings on the lead hazard in homes reported elsewhere in this report incorporate the

results of the analyses of this chapter. That is, the raw MAP/XRF readings have been corrected for

measurement bias and censoring, and the misclassifications due to measurement variation and sampling

within dwelling units have been corrected. Chapter 2 presents the national estimate (83 percent) of

prevalence of lead-based paint in privately-owned housing. Without the corrections of this chapter, the

estimate would have been 74 percent.
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5. CONCLUSIONS

5.1 Major Conclusions

This section presents a brief discussion of the major conclusions to be derived from the experience

of the national survey.

5.1.1 Study Findings

Lead-based paint is widespread in housing. An estimated 64 million (± 7 million) homes, 83

percent (± 9%) of the privately owned housing units built before 1980, have lead-based paint somewhere

in the building. Twelve million (± 1 million) of these homes are occupied by families with children under

the age of seven years old. An estimated 49 million privately owned homes have lead-based paint in their

interiors. There are no significant differences in the prevalence of lead-based paint by type of housing,

market value of the home, amount of rent payment, household income, or geographic region.

Thirteen million homes - 17 percent of the pre-1980 stock - have dust lead levels in excess of the

federal guidelines, regardless of whether or not they have lead-based paint. However, excessive dust lead

levels are associated with the presence of damaged lead-based paint. Fourteen million homes, 19 percent

of the pre-1980 housing stock, have more than five square feet of damaged lead-based paint. Nearly half

of them (47 percent) have excessive dust lead levels.

Although a large majority of pre-1980 homes have lead-based paint, most of them have relatively

small areas of surfaces covered with it. The average privately-owned housing unit with lead-based paint

has an estimated 601 square feet of it on interior surfaces and 869 square feet (per unit) on exterior

surfaces. Over half of the leaded paint is on walls, ceilings, and floors. The amounts of lead-based paint

per housing unit vary with the age of the dwelling unit. Pre-1940 units have, on average, about three

times as much lead-based paint as units built between 1960 and 1979.

Lead paint is even more widespread in public housing; 86 percent (± 8%) of all pre-1980 public

housing family units have lead-based paint somewhere in the building. While most public housing units

have some lead-based paint, most of them have small amounts of it. The average public housing unit with

lead-based paint has an estimated 367 square feet on interior surfaces and 133 square feet (per unit) on

exterior surfaces. Most of the interior lead-based paint is on walls, while very little of the exterior walls

are painted.

5.1.2 Impact of Measurement Error and Lead Loading Variation on the Data Analysis

The data analyses and reports of findings should incorporate instrument and laboratory

measurement error. The MAP/XRF instrument produced readings with measurement errors. They were

systematically different from the actual lead concentrations in the painted surfaces and had random

variation. Similarly, the laboratory protocols used to measure the lead in dust and soil had measurement

errors. These measurement errors can induce systematic errors in the estimated extent of the lead hazard

from paint, dust and soil, and can also result in underestimates of the uncertainty in the estimated hazard.

Therefore, the field procedures must provide for the collection of the QA data necessary to estimate the

measurement errors and their impact on the study findings. Further, the data analyses must explicitly

estimate and correct for the impact of the measurement errors.

The data analyses and reports of findings should take account of the inherent variation in the

painted surfaces. In the national survey, it was not possible to test for the lead content of every painted

surface in every sampled housing unit. Consequently, surfaces were sampled. This sampling protocol
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was designed to control the project costs and respondent burden by controlling the amount of time

required for an inspection. However, it did not adequately provide for the estimation of variation in lead

concentrations within surfaces, between surfaces in the same room, and between rooms. These sources of

variation need to be addressed to produce accurate estimates of the uncertainty in the national estimates.

It is therefore recommended that multiple MAP/XRF readings be taken at randomly selected locations on

a subset of the selected surfaces; at two or more components of the same type in the same room; and in

two wet rooms and two dry rooms. Although it may not be feasible to do this in all homes, a subset

should be selected for these additional readings.

5.1.3 Use of the Spectrum Analyzer MAP/XRF

In contrast to the HUD Interim Guidelines, substrate correction was a necessary step in the

accurate determination of the presence and amount of lead-based paint on surfaces, when using the

MAP/XRF. As discussed in Chapter 4, in the national survey, the MAP/XRF generally produced

readings that were systematically different from the amount of lead in the paint being tested.

Consequently, substrate corrections are needed to obtain accurate measurements of lead loadings. There

are two possible ways to do this:

1. Take frequent validation readings and analytically correct the readings using methods as

described in Appendix II. Readings need to be done on three or more different shims,

however, not just two shims as in the national survey. With only two shims, only a linear

model can be used to correct the MAP/XRF readings. It is possible, however, that a nonlinear model better describes the relationship between the readings and the actual lead

concentrations in the painted surfaces.

2. Perform substrate corrections in the field. The HUD Interim Guidelines describe substrate

correction procedures appropriate for direct reading MAP/XRFs, not the spectrum analyzer

MAP/XRF.

5.2 Additional Conclusions and Recommendations

The main purpose of this section is to identify selected lessons learned during the conduct of the

national survey and to develop recommendations for future field operations. The objective of the

following recommendations is to improve the representativeness and statistical validity of the data, e.g.,

develop methods to enhance respondent participation. Additional recommendations are presented in

Appendix II, Chapter 4.

Applicability of Recommendations

The national survey operated under constraints that are not typical of other lead-based paint

studies. Therefore, some of the following recommendations would not be appropriate under other

research designs. For example, most lead studies are conducted in a single locality, alleviating the

problems associated with moving teams and equipment around the nation under a tight schedule. The

units in the national survey were randomly selected from the national population of dwelling units; most

other studies limit themselves to a smaller, targeted population of units which have some underlying

rationale for being included, e.g., they were FHA-mortgaged properties or they were in a targeted area of

an inner city. A rationale for each recommendation is provided and the reader must use his or her

judgment in determining if the recommendation is appropriate for another design.

All listing and screening should be completed before beginning unit inspections. Completion

of listing and screening before beginning unit inspections means that the full sample frame can be
5-3

developed before sampling is begun. Because of the tight field schedule of the national survey, it was

necessary to begin inspections before listing and screening were completed in some counties. Although it

was possible to take samples from completed counties based on estimates of the final national distribution

of eligible housing, it was necessary after screening was totally completed to adjust the final sample to the

actual distribution. There were two ways to accomplish this: retroactively adjust the sample in the

counties which had been previously sampled; or sample the remaining counties to balance the sample to

the national distribution. Although the former approach yields a better sample statistically, it would have

created costs that were deemed to outweigh the gain in statistical power. The survey adopted the second

course, adjusting the sample in the counties that had not yet been sampled.

When dealing with PHAs, interviewers should closely coordinate with the PHA

representative. Coordination with the PHA management staff is imperative to effective sampling and

inspection of public housing. To ensure that all responsible and affected parties are involved in the

process, it is advisable to establish a liaison with both a PHA headquarters representative and the manager

of the specific housing project. Often teams met the PHA representative at the PHA office and then went

to the site. The PHA staff "smoothed" the way many times. In neighborhoods where the inspection teams

felt unsafe, PHA staff provided a vital service as escorts. Because the PHA staff are busy, every effort

must be made to accommodate their involvement. For example, PHA offices often are not located close

to the dwelling unit. Inspection teams should schedule their time to allow them to meet the PHA staff at

the PHA office and go from there to the dwelling unit. The PHA representatives typically tried to inspect

as many units on each trip as possible. This consideration, combined with frequent unexpected delays,

suggests that the inspection team should not schedule other inspections too soon after the PHA work, to

avoid schedule conflicts. Upon meeting a PHA representative in the field, the inspection team should not

assume that he or she has been fully briefed on the study or the team's mission. The interviewer needs to

go over the objectives and procedures of the survey and the importance of the PHA dwelling unit

inspections.

For public housing dwelling unit sampling, several additional weeks should be allowed for

dwelling unit sample selection in large PHAs. The larger the PHA, the longer time it took to select the

dwelling units. The reasons varied, e.g., the contact was on vacation, there was difficulty finding the

contact, the contact needed authorization, etc. Without exception, selection of PHA dwelling units in the

five largest PHAs in the sample took several weeks longer than it did for the 25 other PHAs.

Field staff should be trained to respond to anyone's questions concerning what they are doing

and what the study is about. Do not attempt to use local police or similar agencies, or the regional

HUD office, to substantiate or verify presence or activities. In the national survey each field person

carried an ID badge, copies of the license that allowed him to handle the MAP/XRF and its radioactive

source, endorsement/introductory letters from survey and agency principals, the 800 number for the

survey coordinator, and a number for the Washington HUD representative. Field staff were questioned on

several occasions by police officers, building managers, or nearby residents. The documentation

materials listed above explained and substantiated the activities of the inspection team and proved

invaluable. Although it seems like a good idea, contacting local police in advance and then referring

questioners to the police can lead to a bigger problem; i.e., the police contacts inadvertently denying

knowledge of the survey. If the person who gets the call at the police station has not been apprised of the

study, he or she will deny knowing anything about it, even though the police department has been

informed of the activities. There is also a problem with overlapping jurisdictions. The study might notify

the county sheriff, although the inquiry comes into the state police.

The analytic model concerning dust analysis and pathways needs to be fully specified before

an adequate dust sampling protocol can be designed. Dust sampling and test result analysis are the

subject of continuing investigations. Insufficient dust was a recurring problem in the field. Outside of

insufficient dust, there were few field problems encountered with dust sampling. A traveling team
5-4

operates under two major constraints -- it must carry its own equipment and it must limit its time in the

dwelling unit to a reasonable length. Getting more dust by using a bigger, more powerful vacuum or

vacuuming a larger area were limited options. The vacuum carried by the survey team weighed ten

pounds, plus tubing, nozzles, and extension cords. The survey found that it took four minutes to

completely collect a dust sample (vacuuming and re-vacuuming a 4-square-foot area as specified in the

dust sampling protocol). A bigger vacuum or more time spent vacuuming were not reasonable in the

context of the national survey. At one point in the procedure design stage it was suggested that in-field

technicians evaluate the quantity of dust collected in a cassette. They would collect more dust in the

cassette if they determined there was insufficient dust. This suggestion proved to be impractical. First,

inspectors could not reliably determine by visual inspection if enough dust had been collected. Second,

movement of the cassette while attached to the vacuum could cause dust to fall out of the cassette. Third,

allowing the technician individual discretion to collect samples would lead to inconsistencies in the

procedure and findings. Last, the amount of time spent vacuuming had to be limited to keep the visit to a

reasonable length. Therefore, this suggestion was not implemented in the survey. A final suggested

approach to increasing dust sample yield was "wet wipe" testing, used in conjunction with or following

vacuuming, to pick up leftover dust. This technique would not have improved effective yield, because

wet wipe test results could not be compared or added in any meaningful way to vacuumed dust sampling

results. Static electricity posed a problem to the inspection team. Dust would cling to the vacuum nozzle,

the edges of the template, etc. Efforts were made to build the template out of a material that did not

accumulate static electricity but the phenomenon still occurred.

The MAP/XRF reading can be taken at any convenient place on a sampled architectural

component; valid sampling does not require readings of a randomly selected spot on the

component. This eliminates readings being taken in hard-to-reach locations, such as corners. The

original design called for sampling a random location on the surface of a component for testing. Though

this is subject to further verification, it appears that components with common paint history produced

similar MAP/XRF readings. Another stage of sampling would significantly burden the inspection

process. Correct assessment of "common paint history" is more pivotal here.

All MAP/XRF readings should be recorded on paper by the inspector. The MAP/XRF used in

the national survey was programmed to store the spectrum results in memory. Serious problems were

encountered, though, when the memory was in use. The memory would fill up rapidly and the MAP/XRF

would stop operating. The equipment had to be turned off, and then back on, in order to restore

operation. All memory was lost in the process. The need to link readings to a location necessitated

recording of a certain amount of data on paper in any event, so that recording MAP/XRF readings on

paper involved little extra effort. The equipment problem aside, using the MAP/XRF's on-board

electronic storage necessitates some procedures for downloading memory contents during the field period.

In practice it did not prove reasonable or practical to return the MAP/XRF to the survey operations office

periodically for downloading. Teaching field staff how to download the memory and transmit it to the

field operations office would have meant providing them with a properly-configured PC and modem in

the field and providing PC training. Adding responsibilities and equipment to the technicians' load was

deemed inadvisable.