Economic News Release

Union Membership Technical Note

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Technical Note

   The estimates in this release are obtained from the Current Population
Survey (CPS), which provides basic information on the labor force, employ-
ment, 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 households.  The union membership and earn-
ings 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.
The data in this release are annual averages.

   Union membership data for 2007 are not strictly comparable with data
for 2006 and earlier years because of the introduction of updated popula-
tion controls with the release of January data.  The effect of the revised
population controls on the union membership estimates is unknown.  However,
the effect of the new controls on the monthly CPS estimates was to increase
the December 2006 employment level by 153,000 and the unemployment level by
10,000.  The updated controls had little or no effect on unemployment rates
and other ratios.  For additional information, see "Adjustments to Household
Survey Population Estimates in January 2007" in the February 2007 issue of
Employment and Earnings, available on the Internet at http://www.bls.gov/
cps/cps07adj.pdf.

   Information in this release will be made 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 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 de-
pending upon 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 direction of the movements in state union mem-
bership 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 infor-
mation, and errors made in the collection or processing of the data.

   For a full discussion of the reliability of data from the CPS and infor-
mation on estimating standard errors, see the Household Data section of the
"Explanatory Notes and Estimates of Error" at http://www.bls.gov/cps/eetech_
methods.pdf.



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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.

   Represented by unions.  Data refer to union members, as well as workers who
have no union affiliation but whose jobs are covered by a union or an employee
association contract.

   Usual weekly earnings.  Data represent earnings before taxes and other deduc-
tions 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, respond-
ents 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, but, for the purposes of the union membership and
earnings series, excludes all self-employed persons, regardless of whether or not
their businesses are incorporated.

   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.

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