Technical Note The estimates in this release are based on annual average data from the Current Population Survey (CPS), a national sample survey of about 60,000 households conducted monthly for the Bureau of Labor Statistics by the U.S. Census Bureau. The information relates to the labor force status of persons 16 years old and over in the civilian noninstitutional population during an "average" week of the year. The data for 2010 presented in this release are not strictly comparable with data for 2009 and earlier years because of the introduction in January 2010 of revised population controls used in the CPS. The effect of the revised popula- tion controls on the family estimates is unknown. However, the effect of the new controls on the monthly CPS estimates was to decrease the December 2009 em- ployment level by 243,000 and the unemployment level by 5,000. The updated controls had little or no effect on unemployment rates and other ratios. Addi- tional 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 de- pending 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 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. A full discussion of the reliability of data from the CPS and information on estimating standard errors is available on the BLS Web site at wwww.bls.gov/cps/documentation.htm#reliability. Definitions Definitions of the principal terms used in this release are presented below. Family. A family is a group of two or more persons residing together who are related by birth, marriage, or adoption. The count of families is for "primary" families only, that is, the householder and all other persons re- lated to and residing with the householder. Families are classified either as married-couple families or as families maintained by women or men without spouses. Householder. The householder is the family reference person. This is the person (or one of the persons) in whose name the housing unit is owned or rented. The relationship of other individuals in the household is defined in terms of relationship to the householder. The race or ethnicity of the family is determined by that of the householder. Married, spouse present; other marital status. These terms denote the marital status of individuals at the time of interview. Married, spouse present, refers to husbands and wives living together in the same house- hold, even though one may be temporarily absent on business, on vacation, on a visit, in a hospital, or for other reasons. Other marital status includes persons who are never-married; married, spouse absent; separated; widowed; or divorced. Separated includes persons with legal separations, those living apart with intentions of obtaining a divorce, and other people living apart because either the husband or wife was employed and living at a considerable distance from home, was serving away from home in the Armed Forces, had moved to another area, or had a different place of residence for any other reason except separation as defined above. Children. Data on children refer to own children and include sons, daughters, step-children, and adopted children, of the husband, wife, or person maintaining the family. Not included are nieces, nephews, grand- children, other related children, and all unrelated children living in the household. Employed. Employed persons are (a) all those who, during the survey reference week, did any work at all as paid employees, worked in their own business, profession, or on their own farm, or who worked 15 hours or more as unpaid workers in a family-operated enterprise; and (b) all those who did not work but had jobs or businesses from which they were temporarily absent due to illness, bad weather, vacation, child-care problems, labor disputes, or personal reasons, whether or not they were paid for the time off and whether or not they were seeking other jobs. Unemployed. The unemployed are persons who had no employment during the reference week, were available for work at that time, and had made specific efforts to find employment sometime during the 4-week period ending with the reference week. Persons who were waiting to be recalled to a job from which they had been laid off need not be looking for work to be classified as unemployed. Civilian labor force. The civilian labor force comprises all persons classified as employed or unemployed. Unemployment rate. The unemployment rate is the number unemployed as a percent of the civilian labor force. Labor force participation rate. The labor force participation rate is the labor force as a percent of the population.