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pdfSurvey Methods and Reliability Statement for the May 2008 Occupational
Employment Statistics Survey
Introduction
The Occupational Employment Statistics (OES) survey is a mail survey measuring occupational
employment and wage rates for wage and salary workers in nonfarm establishments in the 50 States and
the District of Columbia. Guam, Puerto Rico, and the Virgin Islands are also surveyed, but their data are
not included in national estimates.
About 6.8 million in-scope establishments are stratified within their respective States by substate
area and industry. Substate areas include all officially defined metropolitan areas and one or more
nonmetropolitan areas. The North American Industry Classification System (NAICS) is used to stratify
establishments by industry.
Probability sample panels of about 200,000 establishments are selected semiannually. Most
responses are obtained through mail, telephone contact, and e-mail or other electronic means.
Respondents report their number of employees by occupation across 12 wage bands. The Standard
Occupational Classification (SOC) system is used to define occupations.
Estimates of occupational employment and occupational wage rates are based on a rolling 6-panel
(or 3-year) cycle. The final in-scope post-collection sample size when six panels are combined is
approximately 1.1 million establishments. Total 6-panel unweighted employment covers approximately
81 million of the total employment of 136 million.
Occupational and industrial classification systems
The occupational classification system
The U.S. Office of Management and Budget’s Standard Occupational Classification (SOC) system is used
to define occupations. The survey uses the system to categorize workers across 22 major occupational
groups spanning 801 detailed occupations. More information about the SOC system can be found at
www.bls.gov/soc/socguide.htm.
The industrial classification system
The 2008 OES survey estimates are the first to use the 2007 North American Industry Classification
System (NAICS). More information about NAICS can be found at the BLS Web site
www.bls.gov/bls/naics.htm or in the 2007 North American Industry Classification System manual. Each
establishment in the survey is assigned a 6-digit NAICS code based on its primary economic activity.
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Industrial scope and stratification
The survey covers the following NAICS industry sectors:
11
Logging (1133), support activities for crop production
(1151), and support activities for animal production (1152) only
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]
Federal Government Executive Branch (assigned industry code 999100)
State government (assigned industry code 999200)
Local government (assigned industry code 999300)
These sectors are stratified into about 340 industry groups at the 4- or 5-digit NAICS level of detail.
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Concepts
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 refers to the number of workers who can be classified as full- or part-time employees,
including workers on paid vacations or other types of paid leave; salaried officers, executives, and staff
members of incorporated firms; employees temporarily assigned to other units; and non-contract
employees for whom the reporting unit is their permanent duty station regardless of whether that unit
prepares their paychecks.
The OES survey includes all full- and part-time wage and salary workers in nonfarm industries. Selfemployed workers, owners and partners in unincorporated firms, household workers, and unpaid family
workers are excluded.
Occupations are classified based on work performed and on required skills. Employees are assigned to an
occupation based on the work they perform and not on their education or training. For example, an
employee trained as an engineer but working as a drafter is reported as a drafter. Employees who perform
the duties of two or more occupations are reported in the occupation that requires the highest level of skill
or in the occupation where the most time is spent if there is no measurable difference in skill
requirements. Working supervisors (those spending 20 percent or more of their time doing work similar
to the workers they supervise) are classified with the workers they supervise. Workers receiving on-thejob training, apprentices, and trainees are classified with the occupations for which they are being
trained.
A wage is money that is paid or received for work or services performed in a specified period. Base rate
pay, cost-of-living allowances, guaranteed pay, hazardous-duty pay, incentive pay such as commissions
and production bonuses, tips, and on-call pay are included in a wage. Back pay, jury duty pay, overtime
pay, severance pay, shift differentials, non-production bonuses, employer costs for supplementary
benefits, and tuition reimbursements are excluded. Employers are asked to classify each of their workers
into an SOC occupation and one of the following 12 wage intervals:
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Wages
Interval
Hourly rate intervals
Annual rate intervals
Range A
Under $7.50
Under $15,600
Range B
$7.50 to $9.49
$15,600 to $19,759
Range C
$9.50 to $11.99
$19,760 to $24,959
Range D
$12.00 to $15.24
$24,960 to $31,719
Range E
$15.25 to $19.24
$31,720 to $40,039
Range F
$19.25 to $24.49
$40,040 to $50,959
Range G
$24.50 to $30.99
$50,960 to $64,479
Range H
$31.00 to $39.24
$64,480 to $81,639
Range I
$39.25 to $49.74
$81,640 to $103,479
Range J
$49.75 to $63.24
$103,480 to $131,559
Range K
$63.25 to $79.99
$131,560 to $166,399
Range L
$80.00 and over
$166,400 and over
3-year survey cycle of data collection
The survey is based on a probability sample drawn from a universe of about 6.8 million in-scope
establishments stratified by geography and industry. The sample is designed to represent all nonfarm
establishments in the United States.
The OES survey allocates and selects a sample of approximately 200,000 establishments
semiannually, with the exception of May 2008, when about 174,000 establishments were sampled due to
budget cuts. Semiannual samples are referred to as panels. To the extent possible, private sector units
selected in any one panel are not sampled again in the next five panels.
The survey is conducted over a rolling 6-panel (or 3-year) cycle. This is done in order to provide
adequate geographic, industrial, and occupational coverage. Over the course of a 6-panel (or 3-year)
cycle, approximately 1.2 million establishments are sampled. In this cycle, data collected in May 2008 are
combined with data collected in November 2007, May 2007, November 2006, May 2006, and November
2005.
For a given panel, survey questionnaires are initially mailed out to almost all sampled establishments.
State workforce agency staff may make personal visits to some of the larger establishments; however,
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these are limited due to cost and time constraints. Three additional mailings are sent to nonrespondents at
approximately 4-week intervals. Telephone or e-mail follow-ups are made to nonrespondents.
Censuses of Federal and State Government are collected annually.
A census of the executive branch of the Federal Government and the U.S. Postal Service (USPS) is
collected annually in June from the U.S. Office of Personnel Management (OPM) and the U.S. Postal
Service. Data from only the most recent year are retained for use in OES estimates.
In each area, a census of State government establishments, except for school and hospitals, is
collected annually every November. Data from only the most recent year are retained for use in OES
estimates.
A probability sample is taken of local government establishments, except for hospitals, in every State
except Hawaii.
A census of Hawaii’s local government is collected each November. All Hawaii local-governmentowned establishments are included, except for schools and hospitals.
A census of publicly- and privately-owned hospitals is collected over the 3-year period.
A probability sample of schools owned by State or local government, as well as schools in the private
sector, is taken over the 3-year period.
Sampling procedures
Frame construction
The sampling frame, or universe, is a list of about 6.8 million in-scope nonfarm establishments that file
unemployment insurance (UI) reports to the State workforce agencies. Employers are required by law to
file these reports to the State where each establishment is located. Every quarter BLS creates a national
sampling frame by combining the administrative lists of unemployment insurance reports from all of the
States into a single database called the Longitudinal Data Base (LDB). Every six months, OES extracts
the administrative data for establishments that are in scope for OES from the most current LDB. LDB
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files were supplemented with frame files covering Guam and rail transportation (NAICS 4821) because
these establishments are not covered by the UI program.
Construction of the sampling frame includes a process where establishments that are linked together
into multiunit companies are assigned to either the May or November sample. This prevents BLS from
contacting large multiunit companies more than once per year. Furthermore, the frame is matched to the 5
prior sample panels, and units that have been previously selected in the 5 prior panels are marked as
ineligible for sampling for the current panel.
2. Stratification
Establishments on the frame are stratified by geographic area and industry group.
Geography—626 Metropolitan Statistical Areas (MSAs), metropolitan divisions, and
nonmetropolitan or balance-of-State (BOS) areas are specified. MSAs and metropolitan divisions
are defined and mandated by the Office of Management and Budget. Each officially defined
metropolitan area within a State is specified as a substate area. Cross-State MSAs have a separate
portion for each State contributing to that MSA. In addition, States may specify up to four
residual balance-of-State areas to cover the remaining non-MSA portion of their state.
Industry—335 industry groups are defined at the NAICS 4- or 5-digit level.
Ownership – Beginning in November of 2006, schools are also stratified by State government,
local government, or private ownership.
At any given time, there are about 174,000 nonempty State/MSA/BOS-by-NAICS4/5 strata on the
frame. When comparing nonempty strata between frames, there may be substantial frame-to-frame
differences. The differences are due primarily to normal establishment birth and death processes and
normal establishment growth and shrinkage. Other differences are due to NAICS reclassification and
changes in geographic location.
A small number of establishments indicate the State in which their employees are located, but do not
indicate the specific MSA or BOS area in which they are located. These establishments are also sampled
and used in the calculation of the statewide estimates. They are not included in the estimates of any area.
Therefore, the sum of the employment in the MSAs and BOS areas within a State may be less than the
statewide employment.
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Allocation of the sample to strata
Each State is assigned a fixed overall sample size. The frame is stratified into 174,000 nonempty
State/MSA/BOS-by-NAICS4/5 strata. Each time a sample is selected, a 6-panel allocation of the 1.2
million sample units among these strata is performed. The largest establishments are removed from the
allocation because they will be selected with certainty once during the 6-panel cycle. For the remaining
noncertainty strata, a set of minimum sample size requirements based on the number of establishments in
each cell is used to ensure coverage for industry and MSAs. For each State/MSA/BOS-by-NAICS4/5
stratum, a sample allocation is calculated using a power allocation. Two factors influence the power
allocation. One is the square root of the employment size of each stratum. In general, strata with higher
levels of employment are allocated more sample than strata with lower levels of employment.
The other is a measure of the occupational variability of the industry. The occupational variability of
an industry is measured by computing the coefficient of variation (CV) for each occupation within the
90th percentile of occupational employment in a given industry, averaging those CVs, and then calculating
the standard error from that average CV. Using this measure, industries that tend to have greater
occupational variability will get more sample than industries that are more occupationally homogeneous.
The actual 6-panel sample allocation is the larger of the minimum sample allocation and the power
allocation. To determine the current single panel allocation, the 6-panel allocation is divided by 6 and the
resulting quotient is randomly rounded. Note: for panels prior to May 2007, sample allocation was
calculated proportional to the employment in each stratum. The power allocation described above
replaces this proportional allocation method.
Sample selection
Sample selection within strata is approximately proportional to size. In order to provide the most
occupational coverage, establishments with higher employment are more likely to be selected than those
with lower employment; some of the largest establishments are selected with certainty. The unweighted
employment of sampled establishments makes up approximately 61 percent of total employment.
Permanent random numbers (PRNs) are used in the sample selection process. To minimize sample
overlap between the OES survey and other large surveys conducted by the U.S. Bureau of Labor
Statistics, each establishment is assigned a PRN. For each stratum, a specific PRN value is designated as
the “starting” point to select a sample. From this “starting” point, we sequentially select the first ‘n’
eligible establishments in the frame into the sample where ‘n’ denotes the number of establishments to be
sampled.
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Single panel weights (sampling weights)
Sampling weights are computed so that each panel will roughly represent the entire universe of
establishments.
Federal Government, USPS, and State government units are assigned a panel weight of 1. Other
sampled establishments are assigned a design-based panel weight, which reflects the inverse of the
probability of selection.
National sample counts
The combined sample for the May 2008 survey is the equivalent of six panels. The sample allocations
excluding Federal Government and U.S. Postal Service (USPS) for the panels in this cycle are:
173,853 establishments* for May 2008
203,006 establishments for November 2007
201,778 establishments for May 2007
202,508 establishments for November 2006
202,734 establishments for May 2006
202,641 establishments for November 2005
*NOTE: The May 2008 panel had a sample cut, due to budget shortfalls.
The May 2008 sample includes 8,049 Federal and USPS units. The combined sample size for the May
2008 estimates is approximately 1.2 million establishments, which includes only the most recent data for
Federal and State Government. Federal and State Government units from older panels are deleted to avoid
double counting.
Response and nonresponse
Response
Of the approximately 1.2 million establishments in the combined initial sample, 1,097,947 were viable
establishments (that is, establishments that are not outside the scope or out of business). Of the viable
establishments, 859,099 responded and 238,848 did not—a 78.25 percent response rate. The response rate
in terms of weighted sample employment is 74.28 percent.
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Nonresponse
Nonresponse is a chronic problem in virtually all large-scale surveys because it may introduce a bias in
estimates if the nonrespondents tend to differ from respondents in terms of the characteristic being
measured. To partially compensate for nonresponse, the missing data for each nonrespondent are imputed
using plausible data from responding units with similar characteristics.
Establishments that do not report occupational employment data are called “unit” nonrespondents.
Establishments that report employment data but fail to report some or all the corresponding wages are
called “partial” nonrespondents. Missing data for unit nonrespondents are imputed through a two-step
imputation process. Missing data for partial nonrespondents are imputed through the second step of the
process only.
Step 1, Impute an occupational employment staffing pattern
For each unit nonrespondent, a staffing pattern is imputed using a nearest-neighbor “hot deck”
imputation method. The procedure links a responding donor establishment to each
nonrespondent. Possible donors are respondents from the current panel and any of the five
previous panels. The nearest-neighbor hot deck procedure searches within defined cells for a
donor that most closely resembles the nonrespondent by geographic area, industry, and
employment size. Ownership is also used in the hospital and education industries. The procedure
initially searches for a donor whose reported employment is approximately the same as the
nonrespondent’s frame employment within the same MSA/BOS and 5-digit NAICS. If more than
one otherwise equally qualified donor is found, a donor from a more recent panel will be selected
over a donor from an older panel. If the search is unsuccessful, the pool of donors is enlarged in
incremental steps by expanding geographic area and industry until a suitable donor is found.
Limits are placed on the number of times a donor can be used.
After a donor has been found, its occupational staffing pattern is used to prorate the
nonrespondent’s frame employment by occupation. The prorated employment is the
nonrespondent’s imputed occupational employment.
Step 2, Impute an employment distribution across wage intervals:
For each “unit” nonrespondent in step 1 or for each “partial” nonrespondent, impute an
employment distribution across wage intervals for occupations without complete wage data. This
distribution, called the wage employment distribution, is imputed as follows:
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Identify the imputation cell for each of the nonrespondent’s occupations. Imputation cells are
initially defined by MSA/BOS, NAICS4/5, and size class from the most recent panel only. For
schools and hospitals, cells are further divided by ownership.
Determine if the imputation cell has enough respondents to compute wage employment
distributions. If not, incrementally enlarge the cell until there are enough respondents.
Use the distributions above to prorate the nonrespondent’s imputed occupational employment
across wage intervals. (Or, for partial respondents, use the distributions above to prorate the
reported occupational employment across wage intervals.)
Estimation Methodology
This section describes the weighting methodology and formulas used for making the estimates. Each
semiannual sample represents roughly one-sixth of the establishments for the full 6-panel sample plan and
is used in conjunction with the previous five semiannual samples in order to create a combined sample of
approximately 1.2 million establishments, which includes only the most recent data for Federal and State
Government.
Reweighting for the combined sample
Employment and wage rate estimates are computed using a rolling 6-panel (3-year) sample. Estimates for
the May 2008 survey were calculated using data from the May 2008, November 2007, May 2007,
November 2006, May 2006, and November 2005 samples. Establishments from each panel’s sample are
initially assigned weights as if one panel were being used to represent the entire population. When the
samples are combined, each sampled establishment must be reweighted so that the aggregated sample
across six panels represents the entire population. Establishments selected with certainty in the 6-panel
cycle are given a weight equal to 1. Noncertainty units are reweighted stratum-by-stratum. This revised
weight is called the 6-panel combined sample weight. The original single-panel sampling weights are
computed so that responses in a stratum could be weighted to represent the entire stratum population. In
one common scenario, six panel samples are combined, and all six panels have sample units for a
particular stratum. A summation of the single-panel weights would over-represent the population by a
factor of six. Because we do not want to over-represent the stratum population, the final weight of each
establishment is set equal to 1/k times its single-panel sampling weight. In general, when six panel
samples are combined, a count of the number of panels with at least one unit selected for a given stratum
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is assigned to k. The 6-panel combined sample weight of each establishment in the stratum is computed
by multiplying its single-panel sampling weight by 1/k.
Benchmarking to QCEW employment
A ratio estimator is used to calculate estimates of occupational employment. The auxiliary variable for the
estimator is the average of the latest May and November employment totals from the Bureau’s Quarterly
Census of Employment and Wages (QCEW). For the May 2008 survey, the auxiliary variable is the
average of May 2008 and November 2007 employment. In order to balance the State need for estimates at
differing levels of geography and industry, the ratio estimation process is carried out through a series of
four hierarchical employment ratio adjustments. The ratio adjustments are also known as benchmark
factors (BMFs).
The first of the hierarchical benchmark factors is calculated in the States for cells defined by
MSA/BOS, NAICS4/5, and employment size class (4 size classes: 1-19, 20-49, 50-249, 250+). For
establishments in the hospital and education industries (NAICS3 equal 622 and 611), the first hierarchical
factor is calculated in the States for cells defined by MSA/BOS, NAICS4/5, employment size class (4 size
classes: 1-19, 20-49, 50-249, 250+), and ownership (State government, local government or privately
owned). If a first-level BMF is out of range, it is reset to a maximum (ceiling) or minimum (floor) value.
First-level BMFs are calculated as follows:
h = MSA/BOS by NAICS4/5
H = State by NAICS4/5
s = employment size classes (1-19, 20-49, 50-249, 250+)
S = aggregated employment size classes (1-49, 50+)
o = ownership (State government, local government or privately owned)
M = average of May and November QCEW
wi = six-panel combined sample weight for establishment i
xi =
total establishment employment
BMFmin = a parameter, the lowest value allowed for BMF
BMFmax = a parameter, the highest value allowed for BMF
hs M hs
hso M hso
w x ,
ihs
i
i
w x ,
ihso
i
i
hS M hS
hSo M hSo
w x ,
ihS
i
i
w x ,
ihSo
i
i
h M h
ho M ho
w x
ih
i
i
w x ,
iho
i
i
then
11
BMF1 , hs
hso , if all hso within h are bounded by BMFmin , BMFmax ,
, if all within h are bounded by BMF , BMF ,
hs
min
max
hs
hSo , if all hSo within h are bounded by BMFmin , BMFmax ,
hS , if all hS within h are bounded by BMFmin , BMFmax ,
ho , if all ho within h are bounded by BMFmin , BMFmax ,
h , if all h within h are bounded by BMFmin , BMFmax ,
BMFmin , if h BMFmin ,
BMF , if BMF
max
h
max
Second-level BMFs are calculated for cells defined within States at the NAICS4/5 level by
summing the product of final weight and first-level BMF for each establishment in the cell. For
establishments in the hospital and education industries (NAICS3 equal 622 and 611), the first hierarchical
of the second-level BMK factor is calculated in the States at the NAICS4/5 and ownership level. Secondlevel BMFs account for the portion of universe employment that is not adequately covered by weighted
employment in first-level benchmarking. Inadequate coverage occurs when “MSA/BOS | NAICS4/5 | size
class” cells have no sample data or when a floor or ceiling is imposed on first-level BMFs. Second-level
benchmarks are calculated as follows:
Ho
M
Ho
hs H
H
MH
BMF2 , H
hs H
wi xi BMF1, hs
ihs
, then
wi xi BMF1, hs
ihs
Ho , if all Ho within H are bounded by BMFmin , BMFmax ,
, if all within H are bounded by BMF , BMF ,
H
H
min
max
BMFmin , if H BMFmin ,
BMFmax , if H BMFmax
Third-level BMFs (BMF3,H) are calculated at the “State | 3-digit NAICS” cell level by summing
the product of final weight, first-level BMF, and second-level BMF for each establishment in the cell. The
third-level BMF also benchmarks by ownership for the hospital and education industries. Fourth-level
BMFs (BMF4,H) are calculated at the “State | 2-digit NAICS” cell level by summing the product of final
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weight, first-level BMF, second-level BMF, and third-level BMF for each establishment in the cell. The
fourth-level BMK factor does not benchmark by ownership. As with second-level BMFs, third- and
fourth-level BMFs are computed to account for inadequate coverage of the universe employment.
A final benchmark factor, BMFi, is calculated for each establishment as the product of its four
hierarchical benchmark factors (BMFi = BMF1 * BMF2 * BMF3 * BMF4). A benchmark weight value is
then calculated as the product of the establishment’s six-panel combined sample weight and final
benchmark factor.
Occupational employment estimates
Benchmark weights are used to compute estimates of occupational employment. Estimates are produced
for cells defined by geographic area, industry group, and size of establishment (i.e., size class). The total
employment for an occupation in a cell is estimated by taking the product of the reported occupational
employment, the 6-panel combined sample weight, and the final benchmark factor for each establishment
in the cell, and summing the product across all establishments in the cell. This sum is the estimate of total
occupational employment in the cell.
The equation below is used to calculate occupational employment estimates for an estimation cell
defined by geographic area, industry group, and size class.
Xˆ ho
w
ih
i
BMFi xio
o
= occupation;
h
= estimation cell;
wi
= six-panel combined sample weight for establishment i;
BMFi
= final benchmark factor for establishment i;
xio
= reported employment for occupation o in establishment i;
Xˆ ho
= estimated employment for occupation o in cell h
Wage rate estimation
Two externally derived parameters are used to calculate wage rate estimates. They are:
the mean wage rates for each of the 12 wage intervals and
wage updating factors (also known as aging factors)
13
Wage rates of workers are reported to the OES survey as grouped data across 12 consecutive, nonoverlapping wage bands. Individual wage rates are not collected.
An illustration: An establishment employs 10 secretaries at the following wage rates:
$ 8/hour — 1 secretary
$ 9/hour — 1 secretary
$12/hour — 2 secretaries
$13/hour — 2 secretaries
$14/hour — 2 secretaries
$16/hour — 1 secretary
$17/hour — 1 secretary
Wage rates for secretaries, however, are reported to the OES survey as follows:
Wage interval A (under $ 7.50/hour) — 0 secretaries
Wage interval B ($ 7.50-$9.49/hour) — 2 secretaries
Wage interval C ($ 9.50-$11.99/hour) — 0 secretaries
Wage interval D ($12.00-$15.24/hour) — 6 secretaries
Wage interval E ($15.25-$19.24/hour) — 2 secretaries
The remaining wage intervals have 0 secretaries.
Because wage rates are collected as grouped data, we must use grouped data formulae to calculate
estimates of mean and percentile wage rates. Assumptions are made when using grouped data formulae.
For the mean wage rate formula, we assume that we can calculate the average wage rate for workers in
each interval. For the percentile wage rate formula, we assume that workers are evenly distributed in each
interval.
Wage data from the following panels — May 2008, November 2007, May 2007, November 2006,
May 2006, and November 2005 — were used to calculate May 2008 wage rate estimates. Wage data from
different panels, however, are not equivalent in real-dollar terms due to inflation and rising living costs.
Consequently, wage data collected prior to the current survey reference period (May 2008) have to be
updated or aged to approximate that period.
14
Determining a mean wage rate for each interval
The mean hourly wage rate for all workers in any given wage interval cannot be computed using grouped
data collected by the OES survey. This value is calculated externally using data from the Bureau’s
National Compensation Survey (NCS). Although smaller than the OES survey in terms of sample size,
the NCS program, unlike OES, collects individual wage data. With the exception of the highest wage
interval, mean wage rates for each panel are calculated using NCS data for the panel's reference year. The
lower boundary of the highest wage interval was $80.00. The mean hourly wage for this interval was
calculated using the average of the 2005, 2006, and 2007 NCS data. The mean hourly wage rate for
interval L (the upper, open-ended wage interval) is calculated without wage data for pilots. This
occupation is excluded because pilots work fewer hours than workers in other occupations. Consequently,
their hourly wage rates are much higher.
Wage aging process
Aging factors are developed from the Bureau’s Employment Cost Index (ECI) survey. The ECI survey
measures the rate of change in compensation for ten major occupation groups on a quarterly basis. The
eleventh, open ended, interval is not aged. Aging factors are used to adjust OES wage data in past survey
reference periods to the current survey reference period (May 2008). The procedure assumes that there are
no major differences by geography, industry, or detailed occupation within the occupational division. The
wage rates for the highest wage interval are not updated.
Mean hourly wage rate estimates
Mean hourly wage is the total weighted hourly wages for an occupation divided by its weighted survey
employment. Estimates of mean hourly wage are calculated using a standard grouped data formula that
was modified to use ECI aging factors.
t
w
z t 5 i z
Rˆ o
i
BMFi yˆ i o
Xˆ o
yˆ i o u z o xi o r c z r
i z
r
o
= occupation
Rˆ o
= mean hourly wage rate for occupation o
z
= panel (or year)
t
= current panel
15
wi
= six-panel combined sample weight for establishment i
BMFi = final benchmark factor applied to establishment i
yˆ i o
= unweighted total hourly wage estimate for occupation o in establishment i
r
= wage interval
Xˆ o
= estimated employment for occupation o
xi o r
= reported employment for occupation o in establishment i in wage interval r
(note that establishment i reports data for only one panel z or one year z)
uz o
= ECI aging factor for panel (or year) z and occupation o
cz r
= mean hourly wage for interval r in panel (or year) z
In this formula, cz r represents the mean hourly wage of interval r in panel (or year) z. The mean is
computed externally using data from the Bureau’s NCS survey.
Percentile hourly wage rate estimates
The p-th percentile hourly wage rate for an occupation is the wage where p percent of all workers earn
that amount or less and where (100-p) percent of all workers earn that amount or more. The wage interval
containing the p-th percentile 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 p-th percentile
wage rate is then estimated using a linear interpolation procedure.
pRo Lr
pRo
j
(U r Lr )
fr
= p-th percentile hourly wage rate for occupation o
r
= wage interval that encompasses pRo
Lr
= lower bound of wage interval r
Ur
= upper bound of wage interval r
fr
= number of workers in interval r
j
= difference between the number of workers needed to
reach the p-th percentile wage rate and the number of
workers needed to reach the Lr wage rate
16
Annual wage rate estimates
These estimates are calculated by multiplying mean or percentile hourly wage rate estimates by a “yearround, full time” figure of 2,080 hours (52 weeks x 40 hours) per year. These estimates, however, may
not represent mean annual pay should the workers work more or less than 2,080 hours per year.
Alternatively, some workers are paid based on an annual basis but do not work the usual 2,080
hours per year. For these workers, survey respondents report annual wages. Since the survey does not
collect the actual number of hours worked, hourly wage rates cannot be derived from annual wage rates
with any reasonable degree of confidence. Only annual wages are reported for some occupations.
Variance estimation
Occupational employment variance estimation
A subsample replication technique called the “jackknife random group” is used to estimate variances of
occupational employment. In this technique, each sampled establishment is assigned to one of G random
groups. G subsamples are created from the G random groups. Each subsample is reweighted to represent
the universe.
G estimates of total occupational employment ( Xˆ hjog ) (one estimate per subsample) are calculated.
The variability among the G employment estimates is a good variance estimate for occupational
employment. The two formulae below are used to estimate the variance of occupational employment for
an estimation cell defined by geographic area and industry group.
G
v ( Xˆ hjo )
( Xˆ
g 1
hjog
Xˆ hjo ) 2
G (G 1)
h
= estimation cell defined by geographic area and industry group
j
= employment size class (1-19, 20-49, 50-249, 250+)
o
= occupation
v ( Xˆ hjo )
= estimated variance of Xˆ hjo
G
= number of random groups
Xˆ hjo
= estimated employment of occupation o in cell h and size class j
17
Xˆ hjog
= estimated employment of occupation o in cell h, size class j, and subsample g
Xˆ hjo
= estimated mean employment for occupation o in cell h and size class j based
on the G subsamples (Note: a finite population correction factor is
applied to the terms Xˆ hjog and Xˆ hjo .)
The variance for an occupational employment estimate in cell h is obtained by summing the variances
v ( Xˆ hjo ) across all size classes j in the cell.
v ( Xˆ ho ) v ( Xˆ hjo )
jh
Occupational mean wage variance estimates
Because the OES wage data are collected in intervals (grouped), we do not capture the exact wage of each
worker. Therefore, some components of the wage variance are approximated using factors developed
from NCS data. A Taylor Series Linearization technique is used to develop a variance estimator
appropriate for OES mean wage estimates. The primary component of the mean wage variance, which
accounts for the variability of the observed sample data, is estimated using the standard estimator of
variance for a ratio estimate. This component is the first term in the formula given below:
1 n h o 1 f h o
2
2
BMK
w
q
q
(
)
i i
io
ho
Xˆ 2
n
1
ih
h
ho
v( Rˆ o ) o
no
1
1
2
o r 2 r
o2r c2r 2 BMK i wi x i o r e2r
Xˆ o r i 1
Xˆ o r
r
Rˆ o
= estimated mean wage for occupation o
v ( Rˆ o )
= estimated variance of Rˆ o
Xˆ o
= estimated occupational employment for occupation o
h
= stratum (area/industry/size class)
fho
= sampling fraction for occupation o in stratum h
nh o
= number of sampled establishments that reported occupation o in stratum h
wi
= six-panel combined sample weight for establishment i
18
BMFi
= final benchmark factor applied to establishment
qi o
= yˆ i o Rˆ o xi o for occupation o in establishment i
yˆ i o
= estimated total occupational wage in establishment i for occupation o
xi o
= reported employment in establishment i for occupation o
qh o
= mean of the qi o quantities for occupation o in stratum h
o r
= proportion of employment within interval r for occupation o;
xi o r
= reported employment in establishment i within wage interval r for occupation o
2
cr
, e2r , and 2 r Within wage interval r, these are estimated using the NCS and,
respectively, represent: the variability of the wage value imputed to each worker;
the variability of wages across establishments; and the variability of wages
within establishments.
Reliability of the estimates
Estimates developed from a sample will differ from the results of a census. An estimate based on a
sample survey is subject to two types of error—sampling and nonsampling error. An estimate based on a
census is only subject to nonsampling error.
Nonsampling error
This type of error is attributable to several causes, such as: errors in the sampling frame; an inability to
obtain information for all establishments in the sample; differences in respondents' interpretation of a
survey question; an inability or unwillingness of the respondents to provide correct information; errors
made in recording, coding, or processing the data; and errors made in imputing values for missing data.
Explicit measures of the effects of nonsampling error are not available.
Sampling errors
When a sample, rather than an entire population, is surveyed, estimates differ from the true population
values that they represent. This difference, or sampling error, occurs by chance, and its variability is
measured by the variance of the estimate or the standard error of the estimate (square root of the
variance). The relative standard error is the ratio of the standard error to the estimate itself.
19
Estimates of the sampling error for occupational employment and mean wage rate are provided
for all employment and mean wage estimates to allow data users to determine if those statistics are
reliable enough for their needs. Only a probability-based sample can be used to calculate estimates of
sampling error. The formulae used to estimate OES variances are adaptations of formulae appropriate for
the survey design used.
The particular sample used in this survey is one of a large number of many possible samples of
the same size that could have been selected using the same sample design. Sample estimates from a given
design are said to be unbiased when an average of the estimates from all possible samples yields the true
population value. In this case, the sample estimate and its standard error can be used to construct
confidence intervals, or ranges of values that include the true population value with known probabilities.
To illustrate, if the process of selecting a sample from the population were repeated many times, if each
sample were surveyed under essentially the same unbiased conditions, and if an estimate and a suitable
estimate of its standard error were made from each sample, then:
1. Approximately 68 percent of the intervals from one standard error below to one standard error above
the estimate would include the true population value. This interval is called a 68-percent confidence
interval.
2. Approximately 90 percent of the intervals from 1.6 standard errors below to 1.6 standard errors above
the estimate would include the true population value. This interval is called a 90-percent confidence
interval.
3. Approximately 95 percent of the intervals from 2 standard errors below to 2 standard errors above the
estimate would include the true population value. This interval is called the 95-percent confidence
interval.
4. Almost all (99.7 percent) of the intervals from 3 standard errors below to 3 standard errors above the
estimate would include the true population value.
For example, suppose that an estimated occupational employment total is 5,000, with an associated
estimate of relative standard error of 2.0 percent. Based on these data, the standard error of the estimate is
100 (2 percent of 5,000). To construct a 95-percent confidence interval, add and subtract 200 (twice the
standard error) from the estimate: (4,800, 5,200). Approximately 95 percent of the intervals constructed in
this manner will include the true occupational employment if survey methods are nearly unbiased.
20
Estimated standard errors should be taken to indicate the magnitude of sampling error only. They
are not intended to measure nonsampling error, including any biases in the data. Particular care should be
exercised in the interpretation of small estimates or of small differences between estimates when the
sampling error is relatively large or the magnitude of the bias is unknown.
Quality control measures
Several edit and quality control procedures are used to reduce nonsampling error. For example, completed
survey questionnaires are checked for data consistency. Follow-up mailings and phone calls are sent out
to nonresponding establishments to improve the survey response rate. Response analysis studies are
conducted to assess the respondents’ comprehension of the questionnaire.
The OES survey is a Federal-State cooperative effort that enables States to conduct their own
surveys. A major concern with a cooperative program such as OES is to accommodate the needs of BLS
and other Federal agencies, as well as State-specific publication needs, with limited resources while
simultaneously standardizing survey procedures across all 50 States, the District of Columbia, and the
U.S. territories. Controlling sources of nonsampling error in this decentralized environment can be
difficult. One important computerized quality control tool used by the OES survey is the Survey
Processing and Management (SPAM) system. It was developed to provide a consistent and automated
framework for survey processing and to reduce the workload for analysts at the State, regional, and
national levels.
To ensure standardized sampling methods in all areas, the sample is drawn in the national office.
Standardizing data-processing activities, such as validating the sampling frame, allocating and selecting
the sample, refining mailing addresses, addressing envelopes and mailers, editing and updating
questionnaires, conducting electronic review, producing management reports, and calculating
employment estimates, have resulted in the overall standardization of the OES survey methodology. This
has reduced the number of errors on the data files as well as the time needed to review them.
Other quality control measures used in the OES survey include:
Follow-up mail and telephone solicitations of nonrespondents, especially critical or large
nonrespondents
Review of schedules to verify the accuracy and reasonableness of the reported data
Adjustments for atypical reporting units on the data file
Validation of the benchmark employment figures and of the benchmark factors
Validation of the analytical tables of estimates at the NAICS4/5 level
21
Confidentiality
BLS has a strict confidentiality policy that ensures that the survey sample composition, lists of reporters,
and names of respondents will be kept confidential. Additionally, the policy assures respondents that
published figures will not reveal the identity of any specific respondent and will not allow the data of any
specific respondent to be imputed. Each published estimate is screened to ensure that it meets these
confidentiality requirements. To further protect the confidentiality of the data, the specific screening
criteria are not listed in this publication.
Data Presentation
OES data are available in several formats from the OES home page at www.bls/gov/oes. The OES
database search tool (www.bls.gov/oes/home.htm#data) allows customers to create customized HTML or
Excel tables using the most recent OES estimates. OES data are also published as HTML tables at
www.bls.gov/oes/home.htm#tables, or can be downloaded as zipped XLS files at
www.bls.gov/oes/oes_dl.htm. Included are cross-industry data for the United States as a whole, for
individual U.S. States, and for metropolitan and nonmetropolitan areas, along with U.S. industry-specific
estimates by 3-, 4- and some 5-digit NAICS levels. Available data elements include estimates of
employment, hourly and annual mean wages, and hourly and annual percentile wages by occupation, as
well as relative standard errors (RSEs) for the employment and mean wages estimates.
When updated estimates become available, a BLS news release makes an announcement
providing a summary of U.S. data. For additional information, contact the OES staff at (202) 691-6569 or
send e-mail to [email protected].
Uses
For many years, the OES survey has been a major source of detailed occupational employment data by
industry for the Nation, for States, and areas. This survey provides information for many data users,
including individuals and organizations engaged in planning vocational education programs, higher
education programs, and employment and training programs. OES data also are used to prepare
information for career counseling, for job placement activities performed at State Workforce Agencies,
and for personnel planning and market research conducted by private enterprises. OES data also are used
by the Department of Labor’s Foreign Labor Certification (FLC) program, which sets the minimum rate
at which workers on work visas in the United States must be paid.
Occupational Employment Statistics Survey
Bureau of Labor Statistics
June, 2009
22
| File Type | application/pdf |
| File Title | Survey Methods and Reliability Statement for the May 2008 Occupational Employment Statistics Survey |
| Subject | Survey Methods and Reliability Statement for the May 2008 Occupational Employment Statistics Survey, Occupational Employment Sta |
| Author | U.S. Bureau of Labor Statistics |
| File Modified | 2009-06-15 |
| File Created | 2009-06-12 |