Technical Note

   The estimates in this release are obtained from the Current Population Survey (CPS),
which provides the 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 house-
holds. 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.

   The Census Bureau introduces adjustments to the population controls for the CPS as
part of its annual update of population estimates. The effect of the revised population
controls on the union affiliation data is unknown. However, the effect of the new con-
trols on the monthly CPS estimates was to increase the December 2011 employment level
by 216,000. The updated controls had little or no effect on unemployment rates and
other ratios. Estimated levels, such as the number of union members for 2012, are not
strictly comparable with estimated levels for 2011. These adjustments to the levels,
however, should have had only negligible effects on union membership rates. Additional
information is available on the BLS Web site at www.bls.gov/cps/documentation.htm#pop.

   Information in this release will be made available to sensory impaired individuals
upon request. Voice phone: (202) 691-5200; Federal Relay Service: (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 depending 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 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.

   For a full discussion of the reliability of data from the CPS and information on
estimating standard errors, see the Household Data section of the "Explanatory Notes and
Estimates of Error" available on the BLS Web site at www.bls.gov/cps/eetech_methods.pdf.

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 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.