Technical Note
The estimates in this release are obtained from the Current Population Survey (CPS),
which provides basic information on the labor force, employment, and unemployment. The
survey is conducted monthly for the Bureau of Labor Statistics by the U.S. Census Bureau
from a scientifically selected national sample of about 60,000 eligible households. The
union membership and earnings data are tabulated from one-quarter of the CPS monthly
sample and are limited to wage and salary workers. All self-employed workers are
excluded.
Beginning in January of each year, data reflect revised population controls used in
the CPS. Additional information about population controls is available on the BLS
website at www.bls.gov/cps/documentation.htm#pop.
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Reliability of the estimates
Statistics based on the CPS are subject to both sampling and nonsampling error. When
a sample, rather than the 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. The state section of this release preserves the long-time practice of
highlighting the state union membership rates and levels regardless of their
statistical significance.
The CPS data also are affected by 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 the data.
Information about the reliability of data from the CPS and guidance on estimating
standard errors is available at www.bls.gov/cps/documentation.htm#reliability.
Union membership questions
Employed wage and salary workers are classified as union members if they answer
"yes" to the following question: On this job, are you a member of a labor union or
of an employee association similar to a union? If the response is "no" to that
question, then the interviewer asks a second question: On this job, are you covered
by a union or employee association contract? If the response is "yes", then these
persons, along with those who responded "yes" to being union members, are classified
as represented by a union. If the response is "no" to both the first and second
questions, then they are classified as nonunion.
Definitions
The principal definitions used in this release are described briefly below.
Union members. Data refer to members of a labor union or an employee association
similar to a union.
Union membership rate. Data refer to the proportion of total wage and salary
workers who are union members.
Represented by unions. Data refer to both union members and workers who report
no union affiliation but whose jobs are covered by a union or an employee
association contract.
Nonunion. Data refer to workers who are neither members of a union nor
represented by a union on their job.
Usual weekly earnings. Data represent earnings before taxes and other deductions
and include any overtime pay, commissions, or tips usually received (at the main job
in the case of multiple jobholders). 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 time 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 of the weeks worked during the past 4 or 5 months.
Median earnings. The median is the amount which divides a given earnings
distribution into two equal groups, one having earnings above the median and the
other having earnings below the median. The estimating procedure places each reported
or calculated weekly earnings value into $50-wide intervals which are centered around
multiples of $50. The actual value is estimated through the linear interpolation of
the interval in which the median lies.
Wage and salary workers. Workers who receive wages, salaries, commissions,
tips, payment in kind, or piece rates. The group includes employees in both the
private and public sectors. Union membership and earnings data exclude all self-
employed workers, both those with incorporated businesses as well as those with
unincorporated businesses.
Full-time workers. Workers who usually work 35 hours or more per week at their
sole or principal job.
Part-time workers. Workers who usually work fewer than 35 hours per week at their
sole or principal job.
Hispanic or Latino ethnicity. Refers to persons who identified themselves in the
enumeration process as being Spanish, Hispanic, or Latino. Persons whose ethnicity
is identified as Hispanic or Latino may be of any race.
United States Department of Labor
