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. 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 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.