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Technical Note

The estimates in this report were obtained from the 

Current Population Survey (CPS), a national monthly 

sample survey of approximately 60,000 households, 

which provides a wide range of information on the labor 

force, employment, and unemployment. Earnings and 

union affiliation data are collected from one-fourth of the 

CPS monthly sample. The survey is conducted for the U.S. 

Bureau of Labor Statistics by the U.S. Census Bureau, using 

a scientifically selected national sample with coverage in all 

50 States and the District of Columbia. 

Material in this report is in the public domain and, with 

appropriate credit, may be reproduced without permission. 

This information is available to sensory-impaired individuals 

upon request. Voice phone: (202) 691-5200; TDD message

referral phone number: 1-800-877-8339

Reliability of the Estimates

Statistics based on the CPS are subject to both sampling and 

nonsampling error. When a sample, rather than an entire 

population, is surveyed, there is a chance that the sample 

estimates may differ from the “true” population values they 

represent. The exact difference, or sampling error, varies 

depending on the particular sample selected, and this variability is measured by the standard error of the estimate. 

There is about a 90-percent chance, or level of confidence, 

that an estimate based on a sample will differ by no more than 

1.6 standard errors from the “true” population value because

of sampling error. BLS analyses are generally conducted at 

the 90-percent level of confidence. 

All other types of error are referred to as nonsampling 

error. Nonsampling error can occur for many reasons, including the failure to sample a segment of the population, inability to obtain information for all respondents in the sample, 

inability or unwillingness of respondents to provide correct 

information, and errors made in the collection or processing 

of data. CPS data also are affected by nonsampling error. 

The full extent of nonsampling error is unknown, but special 

studies have been conducted to quantify some sources of such 

error in the CPS. For further discussion of the reliability of 

data from the CPS and information on estimating standard 

errors, see the “Explanatory Notes and Estimates of Error” 

section of the Bureau of Labor Statistics Employment and 

Earnings publication.

Concepts and Definitions

Concepts used in this report are defined below.

Civilian noninstitutional population. Included are persons 

16 years of age and older residing in the 50 States and the

District of Columbia who are not confined to institutions (for 

example, penal and mental facilities, homes for the aged), 

and who are not on active duty in the Armed Forces.

Civilian labor force. This group comprises all persons classified as employed or unemployed.

Employed persons. Employed persons are those who, during 

the survey week: (a) did any work at all as paid civilians; (b) 

worked in their own business or profession or on their own 

farm; (c) worked 15 hours or more as unpaid workers in a

family business; or (d) were temporarily absent from their 

jobs because of illness, vacation, bad weather, or another 

reason.

Unemployed persons. Unemployed persons are those who 

had no employment during the survey week, were available 

for work at that time, and made specific efforts to find employment sometime in the prior 4 weeks. Persons laid off 

from their former jobs and awaiting recall did not need to be 

looking for work to be classified as unemployed.

Civilian labor force participation rate. This rate is the civilian labor force as a percent of the civilian noninstitutional 

population.

Employment-population ratio. This ratio represents the 

proportion of the population that is employed.

Unemployment rate. This rate represents the number of unemployed persons as a percent of the civilian labor force.

Race. White, black or African American, and Asian are terms 

used to describe the race of persons. Persons in these categories are those who selected that race group only. Data for the 

remaining race categories—American Indian or Alaska Native, Native Hawaiian or Other Pacific Islanders, and persons 

who selected more than one race category—are included in 

totals but are not shown separately because the number of 

survey respondents was too small to develop estimates of 

sufficient quality for publication. In the enumeration process, 

race is determined by the household respondent.
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Hispanic or Latino ethnicity. This term refers to persons 

who identified themselves in the CPS enumeration process as 

being Spanish, Hispanic, or Latino. Persons whose ethnicity 

is identified as Hispanic or Latino may be of any race.

Family. A family is a group of two or more persons residing together who are related by birth, marriage, or adoption. 

Families are classified either as married-couple families or as 

families maintained by women or men without spouses.

Self-employed workers. Self-employed workers are those 

who work for profit or fees in their own business, profession, trade, or farm. Only the unincorporated self-employed 

are included in the self-employed category. Self-employed 

persons whose businesses are incorporated are included in 

wage and salary employment because, technically, they are 

paid employees of a corporation.

Wage and salary workers. These are workers who receive 

wages, salaries, commissions, tips, payment in kind, or piece 

rates. The group includes employees in both the private 

and public sectors but, for purposes of the earnings series, 

excludes all self-employed persons, regardless of whether 

their businesses are incorporated.

Hourly paid workers. Workers who are paid an hourly 

wage are a subset of wage and salary workers, representing 

approximately three-fifths of all wage and salary workers. 

Workers paid by the hour are, therefore, included in the fulland part-time worker tables in this report, along with salaried 

workers and other workers not paid by the hour. (Data for 

workers paid at hourly rates are presented separately.) 

Usual weekly earnings. Data are collected on wages and 

salaries before taxes and other deductions and include any 

overtime pay, commissions, or tips usually received (at the 

principal job in the case of multiple jobholders). Earnings of 

self-employed workers are excluded, regardless of whether 

their businesses are incorporated. Prior to 1994, respondents

were asked how much they usually earned per week. Since 

January 1994, respondents have been asked to identify the

easiest way for them to report earnings (hourly, weekly, 

biweekly, twice monthly, monthly, annually, other) and how 

much they usually earn in the reported period. Earnings 

reported on a basis other than weekly are converted to a 

weekly equivalent. The term “usual” is as perceived by the 

respondent. If the respondent asks for a definition of usual, 

interviewers are instructed to define the term as more than 

half the weeks worked during the past 4 or 5 months.

Medians of weekly earnings. The median is the amount that 

divides a given earnings distribution into two equal groups, 

one having earnings above the median, and the other having 

earnings below the median. The BLS estimating procedure 

for determining the median of an earnings distribution 

places each reported or calculated weekly earnings value 

into a $50-wide interval that is centered on a multiple of 

$50. The value of the median is estimated through a linear 

interpolation of the interval in which the median lies. Overthe-year changes in the medians for specific groups may not 

necessarily be consistent with the movements estimated for 

the overall group boundary. The most common reasons for 

this possible anomaly follow: (1) There could be a change

in the relative weights of the subgroups. For example, the 

medians of both 16- to 24-year-olds and those 25 years

and over may rise, but if the lower earning 16-to-24 age

group accounts for a greatly increased share of the total, 

the overall median could actually fall. (2) There could be 

a large change in the shape of the distribution of reported 

earnings. This could be caused by survey observations that 

are clustered at rounded values, for example, $250, $300, 

or $400. An estimate lying in a $50-wide centered interval 

containing such a cluster, or “spike,” tends to change more 

slowly than one in other intervals. Medians, for example, 

measure the central tendency of a multipeaked distribution 

that shifts over time. As the distribution shifts, the median 

does not necessarily move at the same rate. Specifically, 

the median takes relatively more time to move through a 

frequently reported interval but, once above the upper limit 

of such an interval, it can move relatively quickly to the 

next frequently reported earnings interval. BLS procedures 

for estimating medians mitigate such irregular movements 

of the measures; however, users should be cautious of these 

effects when evaluating short-term changes in the medians, 

as well as in ratios of the medians. 

Hours at work. These are the actual hours worked during 

the reference week. For example, persons who normally 

work 40 hours a week but were off during the Columbus 

Day holiday would be reported as working 32 hours, even 

though they were paid for the holiday.

Usual hours, or usual full- or part-time status. Data on persons “at work” exclude persons who were temporarily absent 

from a job and, therefore, classified in the zero-hours worked 

category, “with a job but not at work.” These are persons who 

were absent from their jobs for the entire week for reasons 

such as bad weather, vacation, illness, or involvement in a 

labor dispute. To differentiate a person’s normal schedule 

from his or her activity during the reference week, persons 

also are classified according to their usual full- or part-time 

status. In this context, full-time workers are those who usually worked 35 hours or more (at all jobs combined). This 

group includes some individuals who worked less than 35 

hours in the reference week for either economic or noneconomic reasons and those who were temporarily absent from 

work. Similarly, part-time workers are those who usually 

work less than 35 hours per week (at all jobs), regardless 

of the number of hours worked in the reference week. This 

may include some individuals who actually worked more 
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than 34 hours in the reference week, as well as those who 

are temporarily absent from work.

Occupation and industry. This information applies to the job 

held during the reference week. Persons with two or more 

jobs are classified in the occupation and industry at which 

they worked the greatest number of hours. The occupational 

and industry classification of CPS data is based on the 2002 

Census Bureau occupational and industrial classification systems which are derived from the 2000 Standard Occupation 

Classification (SOC) and the 2002 North American Industry 

Classification System (NAICS). 

Work experience. These data reflect work activity during the 

calendar year and are obtained from the Annual Social and 

Economic Supplement (ASEC) to the Current Population 

Survey. Persons who worked were those who answered “yes” 

to the following questions from the ASEC: “Did you work 

at a job or business at any time during [the survey reference 

year]?” or “Did you do any temporary, part-time, or seasonal work even for a few days during [the survey reference 

year]?” Since the reference period is a full year, the number 

of persons with some employment or unemployment greatly 

exceeds the average levels for any given month, which are 

based on a 1-week reference period, and the corresponding

annual averages of monthly estimates.

Poverty classification. Poverty statistics presented in this 

report are based on definitions developed by the Social 

Security Administration in 1964 and revised by the Federal interagency committees in 1969 and 191.  Th

definitions originally were based on the U.S. Department 

of Agriculture’s Economy Food Plan and reflected the 

different consumption requirements of families, based 

on factors such as family size and the number of children 

under 18 years of age. The actual poverty thresholds vary

in accordance with the makeup of the family. Poverty 

thresholds are updated each year to reflect changes in the 

Consumer Price Index for All Urban Consumers (CPI-U). 

The thresholds do not vary geographically. For more information on poverty data and thresholds, see http://www.

census.gov/hhes/www/poverty/poverty.html.