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Survey Methods and Reliability Statement for the August 2011 Green

Technologies and Practices Survey

I. Introduction

The Green Technologies and Practices (GTP) survey is a special survey of business establishments

designed to measure the use of technologies and practices that lessen the environmental impact of an

establishment’s production processes. The survey also collects occupational employment and wage data

for wage and salary workers who spent more than half of their time involved in green technologies and

practices during the survey reference period, the pay period including August 12, 2011.

The GTP survey collects information on the BLS process approach to measuring green jobs: jobs in which

workers' duties involve making their establishment's production processes more environmentally

friendly or use fewer natural resources. More information about the BLS green jobs initiative is available

from the green jobs homepage at www.bls.gov/green.

The GTP survey draws its sample primarily from the Quarterly Census of Employment and Wages

(QCEW) state unemployment insurance (UI) files. About 6.7 million establishments in the 50 states and

the District of Columbia were stratified by Census region and 2007 North American Industry

Classification System (NAICS) 2‐digit industry sector. From this sampling frame, a probability sample of

about 35,000 establishments was selected.  

Survey forms were mailed to sampled business establishments. About 70 percent of sampled

establishments responded to the GTP survey. Forty‐seven percent of respondents provided data by

telephone, 37 percent returned the survey form by mail, and the remainder responded by email, fax, or

on the internet.

Respondents were asked whether or not they used each of six green technologies and practices during

the pay period that included August 12, 2011. They were also asked to provide the number of

employees who spent more than half of their time involved in green technologies and practices during

the reference period. For such workers, respondents were asked to provide job titles and brief job

descriptions, as well as the number of workers, by occupation, in each of 12 specific wage intervals. The

wage intervals were defined in terms of both hourly rates and the corresponding annual rates, where

the annual rate for an occupation is calculated by multiplying the hourly wage rate by a typical work

year of 2,080 hours. Respondents were instructed to report part‐time workers at their hourly rates. Full‐

time workers could be reported by either hourly rates or annual salaries, depending on how the worker

was paid.

   
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II. Definitions

Green technologies and practices are technologies and practices that lessen the environmental impact

of an establishment’s production processes. Employers were asked whether they had used each of the

six green technologies and practices listed below during the reference period. Examples were provided

of the types of technologies and practices included in each of the six categories.  

Energy from renewable sources and energy efficiency  

1. Generate electricity, heat, or fuel from renewable sources primarily for use within the

establishment.  

Examples of renewable sources:  

 Wind  

 Geothermal  

 Ocean  

 Landfill gas  

 Biomass  

 Solar  

 Hydropower

 Municipal solid waste  

   

2. Use technologies or practices to improve energy efficiency within the establishment.

Examples:

 Energy Star rated appliances  

 Occupying a LEED (Leadership in Energy and Environmental Design) certified building  

 Energy efficient lighting  

 Programmable thermostats  

 Cogeneration (combined heat and power)

 Energy efficient manufacturing equipment  

Greenhouse gas reduction and pollution reduction and removal  

3. Use technologies or practices in operations to reduce greenhouse gas emissions through

methods other than renewable energy generation and energy efficiency.

Examples:

 Purchase and use of carbon offsets  

 Promotion and/or subsidy of alternative forms of transportation for employees, such as

carpools, fuel efficient vehicles, cycling, or mass transit  

 Implementation of a telework program for employees  
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4. Use technologies or practices to either reduce the creation or release of pollutants or toxic

compounds as a result of operations, or to remove pollutants or hazardous waste from the

environment.

Examples of pollutants or toxic compounds:    

 Carbon monoxide

 Sulfur dioxide  

 Chlorofluorocarbons (CFCs)

 Nitrogen oxides

 Chlorinated hydrocarbons

 Herbicides or pesticides

 Heavy metals  

 Radioactive contamination

Recycling and reuse and natural resource conservation  

5. Use technologies or practices to reduce or eliminate the creation of waste materials as a result

of operations.

Examples:

 Collecting and reusing or recycling waste  

 Managing wastewater  

 Composting solid waste  

 Remanufacturing  

6. Use technologies or practices in operations to conserve natural resources, excluding the use of

recycled inputs in production processes.

Examples:  

 Managing land resources  

 Managing storm water  

 Conserving soil, water, or wildlife  

 Implementing organic agriculture or sustainable forestry practices

An establishment is generally a single physical location at which economic activity occurs (e.g., store,

factory, restaurant, etc.). Each establishment is assigned a 6‐digit NAICS code. When a single physical

location encompasses two or more distinct economic activities, it is treated as two or more separate

establishments if separate payroll records are available and certain other criteria are met.

Employment is defined as the number of full‐ and part‐time workers who are paid a wage or salary,

including paid owners, officers, and staff of incorporated firms and workers temporarily assigned to
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other locations. The survey does not include the self‐employed or owners, partners, and proprietors of

unincorporated firms; unpaid family workers; workers on unpaid leave; workers not covered by

unemployment insurance; and contractors and temporary agency employees not on the sampled

establishment’s payroll.

GTP employment refers to the number of jobs in which workers spend more than half of their time

involved in green technologies and practices. Employees were considered to be involved in green

technologies and practices if they were researching, developing, maintaining, using, or installing green

technologies and practices, or training the establishment’s workers in these technologies and practices.  

An occupation is a set of activities or tasks that employees are paid to perform. Workers are classified

into occupations based on their job duties and, in some cases, on the skills, education, and/or training

required. Workers with similar job duties are classified in the same occupation, regardless of the

industry in which they are employed. The GTP survey uses the 2010 Standard Occupational Classification

(SOC) system to classify workers into occupations.  

Wages are money that is paid or received for work or services performed in a specified period. Wages

for the GTP survey are straight‐time, gross pay, exclusive of premium pay.  

Included in the collection of wage data are:  

 Base rates

 Commissions  

 Cost‐of‐living allowances  

 Deadheading pay  

 Guaranteed pay  

 Hazard pay  

 Incentive pay  

 Longevity pay  

 Over‐the‐road pay (mileage)  

 Piece rates  

 Portal‐to‐portal rates  

 Production bonuses  

 Tips  

Excluded from the wage data are:  

 Attendance bonuses  

 Back pay  

 Clothing allowances  

 Discount  

 Draw  

 Holiday bonuses  
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 Holiday premium pay

 Jury duty pay

 Meal and lodging payments  

 Merchandise discounts  

 Nonproduction bonuses  

 On‐call pay   

 Overtime pay  

 Perquisites  

 Profit‐sharing payments  

 Relocation allowances  

 Severance pay  

 Shift differentials  

 Stock bonuses  

 Tool/equipment allowances  

 Tuition repayment  

 Uniform allowance  

 Vacation pay  

 Weekend premium pay  

 Year‐end bonuses  

III. Sample design  

Frame Creation

The GTP sampling frame has about 6.7 million in‐scope establishments, which includes private and

government establishments in the 50 states and the District of Columbia. The frame is developed

primarily from the state Quarterly Census of Employment and Wages (QCEW) files for the 3rd quarter of

2010. The QCEW includes all business establishments subject to unemployment insurance (UI) tax. In

addition to the QCEW data file, a railroad sampling frame is used.

BLS also conducted research to identify establishments known to be green and has compiled its own

green list through web research and the use of other known green business organization lists. This list

contains about 31,000 establishments and was used as a separate frame in order to target these

establishments; this will be referred to as the green frame in later sections.   

Stratification

Establishments on the frame are stratified by Census region and 2‐digit industry sector (NAICS).  

 Geography—There are four Census regions: Northeast, Midwest, South, and West.  
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 Industry—There are 20 2‐digit industry sectors:

11    Agriculture, forestry, fishing, and hunting

21    Mining

22    Utilities

23    Construction

31‐33 Manufacturing

42    Wholesale trade

44‐45 Retail trade

48‐49 Transportation and warehousing

51    Information

52    Finance and insurance

53    Real estate and rental and leasing

54    Professional, scientific, and technical services

55    Management of companies and enterprises

56    Administrative and support and waste management and

      remediation services

61    Educational services

62    Health care and social assistance

71    Arts, entertainment, and recreation

72    Accommodation and food services

81    Other services, except public administration [private

      households (814) are excluded]

92    Public administration

Sample Allocation

The sample of approximately 35,000 units is allocated into the strata defined above. About 33,000

establishments are allocated to the GTP sample from the QCEW frame. About 2,000 establishments are

allocated from the green frame mentioned above. The sample is allocated according to the following

formula:

1

* h

h H

h

h

X

n N

X 





h = a sampling cell defined by Census Region, 2‐digit NAICS industry (h = 1, 2, ..., H)

N = the national sample size

Xh = the total frame employment of establishments in sampling cell h
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nh = the number of sample units allocated to sampling cell h

For the cell employment Xh, the employment for each establishment is defined as the maximum of that

establishment’s 12 monthly employment values.  The maximum employment is used to define the size

of an establishment in order to eliminate the need for any adjustments due to seasonality. Units with

employment less than or equal to 10 are treated as if they have 10 employees for this procedure.  

Selection

Within each stratum, the sample is selected using a modified probability proportional to estimated

employment size (PPES) method. The employment size for an establishment is determined by the

maximum employment over the prior 12 months of data available from the QCEW. Units with

employment of zero over the 12 months were excluded.

Assignment of Sample Weights

Each sampled establishment is assigned a sampling weight equal to the reciprocal of its probability of

selection in the sample. These weights are later adjusted when nonresponse and benchmark

employment factors are taken into account. These weights are computed so that the sample will

represent the entire universe of establishments.

IV. Estimation

Horvitz‐Thompson Estimator

A Horvitz‐Thompson (HT) estimator is used to estimate GTP employment and the number of

establishments reporting green technologies and practices. Establishments’ reported total employment

and GTP employment figures are used to calculate the employment estimates. Every establishment has

a final weight that is a combination of sampling weights, benchmark factors, and nonresponse

adjustment factors. In order to calculate estimates for the whole population, these final weights are

multiplied by the corresponding variables, such as reported employment, GTP employment, or green

technologies and practices reported.

The estimation levels for the GTP survey are:

 National

 Census region

 2‐digit NAICS sector

 Occupations, detailed and groups
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For estimation cell h, estimates are computed using the following formula:

ሻ௜ݔ כ ௜ݓ݂ሺ ෍ൌ௛ ොݕ

௛א௜

࢏࢝ࢌ = final weight for establishment i

࢏࢞ = reported value for establishment i

This formula is used to compute many different kinds of estimates, such as green employment and

number of establishments reporting green technologies and practices.

Nonresponse Adjustment

For a variety of reasons, some sampled establishments either fail to respond or fail to provide complete,

usable information on the survey form. Both types of establishments are considered nonrespondents,

but are handled differently. Establishments that do not report occupational wage data and green

practices data are considered unit nonrespondents.  Establishments that have missing or zero reported

employment and do not have employment on the QCEW frame are also considered unit

nonrespondents. The nonresponse adjustment factors are calculated to account for these units that did

not provide usable response information. On the other hand, establishments that report occupations

and their totals but fail to report corresponding occupational wage data or establishments that report

only part of the green practices data are called partial nonrespondents, and are imputed according to

procedures detailed in a later section.

Unit nonresponse adjustment was conducted at the Census region/2‐digit NAICS/Size class level. If there

are not enough sample units in the cell, then size classes are collapsed until we get a sufficient number

of units in the cell for nonresponse adjustment calculations. The nonresponse factors are calculated

using the following formula:

ൌ௛ ,௜ܨܣܴܰ

௜ܲܯܧ_ݔܽܯ כ ௜ݓ ೓ఢௌ∑௜

௜ܲܯܧ_ݔܽܯ ೓ כ ௜ݓ ோא௜∑

Max_EMPi = maximum QCEW employment over 12 months of unit i in nonresponse adjustment cell h

wi = sampling weight of unit i in nonresponse adjustment cell h

Sh = sampled establishments in cell h

Rh = usable respondents in cell h
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Benchmarking

The benchmark process ensures that the employment estimates are consistent with employment figures

from the QCEW program. Benchmarking is performed at the Census region/2‐digit NAICS level and is

done after nonresponse adjustment. The weights used in the benchmark calculation are modified by

nonresponse adjustment factors (NRAF). The auxiliary variable for the estimator is the August 2011

employment from the QCEW.  

The benchmark factors are calculated using the following formula:

ൌ௛ ,௜ܨܯܤ

௜ܲܯܧ_݉݇ܤ ೓ఢே∑௜

௜ܲܯܧ_ݐ݌ܴ ೓ כ ோא௜ ௜ܨܣܴܰ כ ௜ݓ ∑

Bmk_EMPi = August QCEW employment for unit i in cell h

Rpt_EMPi = reported employment for unit i

wi = sampling weight of unit i

NRAFi = nonresponse adjustment factor of unit i  

BMFi,h = benchmark factor of unit i in adjustment cell h

Nh = frame establishments in cell h (2011 3rd quarter QCEW)

Rh = usable respondents in cell h

Imputation

Two different types of imputation methods are used for missing data. Nearest neighbor imputation is

used for green technologies and practices and wage distribution imputation is used for reported

occupations that are missing their occupational wage distributions.   

The nearest neighbor imputation method is used to fill in missing green technologies and practices data

for partial nonrespondents. A donor pool of respondents is found that most closely resembles each

nonrespondent by geography, industry, and size. The search begins at the Census region/5‐digit

NAICS/size class level; if a suitable donor pool is not found, the search continues in a hierarchical

manner by expanding the geography, industry, and size class. In addition to the hierarchy, two

additional methods are used to help conceive a donor pool: the green activity match and the

employment distance function methods. The green activity match is used when a unit reports answers to

only some of the green technologies and practices questions. The employment distance function is used

when a unit reports no answers to all of the green technologies and practices questions. In this case, a

distance is computed using the reported employment and reported green employment to find the
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closest donors. Once the donor pool is created, the partial nonrespondent is imputed using the donors’

combined answers to the green technologies and practices questions.

The wage distribution imputation method is used to impute wage distributions for units that report

occupations and employment but not the wage distributions. A donor pool is selected in a similar way as

described above in the nearest neighbor imputation. The search for a donor pool here starts with

establishments reporting wage information for the occupation in the same MSA/4‐digit NAICS/size class

level. If a suitable donor pool is not found, the search continues in a hierarchical manner by expanding

geography, industry, and size class. Once a donor pool is created, the distribution across wage intervals

is computed using the weighted occupational employment of respondents that report that occupation.

The distribution is then used to prorate the nonrespondent’s occupational employment total across the

wage intervals.  

Mean and Median Wage Estimates  

Since the GTP survey collects wage data by wage intervals rather than by wage rate, special procedures

are needed to produce mean and median wage estimates.   

Mean Wage Estimates

Mean wage estimates are calculated using a weighted mean of the 12 wage intervals (A through L). In

order to estimate this, means for the individual wage intervals are needed. These are calculated using

harmonic means for 11 of the 12 wage intervals. The interval mean for the highest, open‐ended interval

is calculated based on data from the BLS National Compensation Survey. For the lowest wage interval,

state‐specific harmonic means are calculated that incorporate each state’s minimum wage.   

The harmonic mean used to compute each interval mean is

ݔഥ ൌఫ

ଶݔ כ ଵݔ כ2

ଶݔ൅ଵݔ

x1 = the lower bound of interval j

x2 = the upper bound of interval j

The mean wage rate for occupation O in estimation cell Ω is:

ҧݔ

௝ ఫ ݌݁݉_ܽ݊݃݁ݎ_ܽ݃݁ݓ כ ഥݔ ሺ ∑ ∑ ൌ௢ ,ஐ

௅

೚,ಈ ௡ሻ௜ݐ݃ݓ_݈݅݊ܽܨ כ ஺ୀ௝

௜ୀଵ

௜ݐ݃ݓ_݈݅݊ܽܨ כ ௝݌݁݉_ܽ݊݃݁ݎ_ܽ݃݁ݓ ሺ∑ ∑ 

௅

௝ୀ஺

௡ಈ,బ

௜ୀଵ ሻ
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ݔഥఫ     = mean wage rate for interval j (j= A, B,...,L)

ݓܽ݃݁_ݎܽ݊݃݁_݁݉݌ = ௝reported occupational employment under wage interval j

ܨ݈݅݊ܽ_ݓ݃ݐ௜     = final weight of unit i  

݊ஐ,௢        = number of units with occupation O in estimation cell Ω

Median Wage Estimates

The median or 50th percentile hourly wage rate for an occupation is the wage where 50 percent of all

workers earn that amount or less and where 50 percent of all workers earn that amount or more. The

wage interval containing the median hourly wage rate is located using a cumulative frequency count of

estimated employment across all wage intervals. After the targeted wage interval is identified, the

median wage rate is then estimated using a linear interpolation procedure. In the GTP survey, weighted

median estimates are calculated where establishment weights are taken into consideration.

Variance

The Green Technologies and Practices survey uses Fay’s modified Balanced Repeated Replication

method to calculate variances. This method splits the sample into halves and multiplies each unit’s

sampling weight by 0.5 or 1.5 based on values from a Hadamard matrix. All estimates are then

computed with these modified sampling weights. This is repeated γ times, with each replicate producing

a different half‐sample and a different set of estimates. These replicates are used to estimate sample

variances using the formula below:

ܸ෠ሺݖ̂ሻ ൌ ଵ

ఊכሺଵି௄ሻమ ∑ ሺݖ̂

௜

ఈ െ ݖ̂

ሻ ఊ ଶ

௜ୀଵ     

̂ݖ

௜

ఈ = i

th replicate estimate of population parameter Z

ݖ̂   =sample‐based estimate of population parameter Z

0.5 ൌ ܭ

γ  = number of replicates (140 in the GTP survey)

   
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V. Quality Control

The GTP survey underwent rigorous design and response testing prior to production. Cognitive

interviews were conducted with establishments thought to have green technologies and practices to

further BLS’s understanding of environmental terminology and relevance. A feasibility study was

conducted to assess both the understanding of the survey’s language and firms’ ability to provide the

requested data. Five test panels were conducted to refine the survey procedures and collection

instruments: mail survey form, fax survey form, email survey form, and internet collection form.

Response analysis surveys were conducted on a small number of respondents and nonrespondents in

each of the five test panels to further understand respondents’ and nonrespondents’ reactions to the

survey questions and their reasons for response or nonresponse.