The Civilian Labor Force includes all persons 16 years of age and older who are employed or are available for employment, except armed services personnel. Unlike employment figures, which are based on establishment surveys that count the number of jobs on establishment payrolls, labor force figures are based on household surveys and reflect the number of individuals who have jobs or are looking for work. These two series diverge because some individuals in the labor force have more than one job (counted once in the labor force but more than once in payroll employment), are self-employed (counted in the labor force but not in payroll employment), commute across state lines to work (counted in the workplace state’s payroll employment but in the residence state’s labor force), or are unemployed (counted in the labor force but not in payroll employment).
The Number Unemployed figure reports civilians who had no employment during the survey week, but were available for work, except for temporary illness, and had made specific efforts to find employment some time during the prior four weeks. Persons are classified as unemployed if they are waiting to be recalled to a job from which they were laid off or are waiting to report to a new job within 30 days.
The Unemployment Rate represents the number of unemployed persons as a percentage of the civilian labor force. U.S. labor force and unemployment data are gathered for BLS by the Census Bureau in its monthly Current Population Survey, a sample of U.S. households designed to represent the civilian noninstitutional population, and are published in the monthly news release The Employment Situation. Labor force and unemployment data for Census regions, divisions, states, and metropolitan areas (including NECTAs) are estimated using a time series modeling approach by state employment security agencies under a federal-state cooperative program. Regional and state unemployment data appear in the monthly news release, Regional and State Employment and Unemployment, while data for 21 NECTAs and 9 NECTA divisions appear in Metropolitan Area Employment and Unemployment. The Federal Reserve Bank of Boston seasonally adjusts NECTA-level unemployment data using the X-11 ARIMA method.
When calendar year data are complete each year, unemployment estimates for state and metro areas (including NECTAs) are revised by BLS and state employment security agencies. Revised data are generally released each March.
Source
U.S. Bureau of Labor Statistics
http://www.bls.gov/cps/home.htm
http://www.bls.gov/lau/home.htm