96

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 may be 

reproduced without permission. This information is available 

to sensory-impaired individuals on 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 generally are 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 Household Data technical documentation provided 

at http://www.bls.gov/cps/eetech_methods.pdf. 

Concepts and Definitions

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, correctional facilities and residential nursing 

and mental health care facilities), 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 survey process, race 

is determined by the household respondent.

Hispanic or Latino ethnicity. This term refers to persons 

who identified themselves in the survey as being Spanish, 
97

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. Unincorporated self-employed are included in 

the self-employed category. Self-employed persons whose 

businesses are incorporated are included in wage and salary 

employment.

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, both those with incorporated 

businesses as well as those with unincorporated businesses.

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 included in the estimates of 

median usual weekly earnings in this report, along with 

salaried workers and other workers not paid by the hour. 

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 to report earnings 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, or 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, $300, $400, 

or $500. 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. For example, medians 

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 (at all 

jobs) 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 worked more than 34 hours in 

the reference week, as well as those who were 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 
98

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). Additional information 

about these classifications is available online at http://www.

bls.gov/cps/cpsoccind.htm. 

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. Estimates of persons who worked were based on 

“yes” responses to the following questions in 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 1981. These definitions 

originally were based on the 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.