Current Population Survey (CPS)
What is the Current Population Survey?
The Current Population Survey (CPS) is a monthly survey of about 60,000 households conducted by the U.S. Census Bureau for the Bureau of Labor Statistics. The CPS is collected with a multi-stage stratified sampling method. Households from all 50 states and the District of Columbia are in the survey for 4 consecutive months, out for 8 months, and then return for another 4 months before leaving the sample permanently. In total, a sample housing unit is interviewed 8 times. The sample represents the civilian non-institutionalized population. CPS can be used to obtain estimates at four geographic levels: (1) the metropolitan level, (2) the state level, (3) the regional level, and (4) the national level. However, the estimates at the metropolitan level are available only for large metropolitan areas.
The CPS is the primary source of information on labor force characteristics of the U.S. population. Respondents are interviewed to obtain information about the employment status of each member of the household 15 years of age and older. Specifically, the CPS collects basic data on employment, unemployment, earnings, hours of work, and other indicators each month. In addition, CPS periodically collects supplemental data on a variety of topics including an annual demographic file; employee benefits; fertility and immigration; health and benefits, job training; work schedules; pensions; schooling and computers; tobacco use; occupational mobility and job tenure; school enrollment; veteran’s; voting and registration; computer and internet use; volunteer workers; food security; child support; lead paint; and landline and cell phone usage.
How do I access CPS data?
Both the basic and supplemental CPS data files can be downloaded from the CPS FTP site (http://www.bls.census.gov/cps_ftp.html), the Census DataFerrett site (http://dataferrett.census.gov/), and National Bureau of Economic Research (NBER) website http://www.nber.org/data/cps_basic.html and http://www.nber.org/data/current-population-survey-data.html). However, of these three sites, only the Census DataFerrett and the NBER site provide SAS, Stata, and SPSS command files to read in the raw data files.
What preparation is needed to use CPS data?
The DataFerrett site allows researchers to conduct simple on-line analyses of CPS data, such as calculating averages or standard deviation, running frequencies and crosstabs, and constructing simple figures. If you are only interested in these analyses, you can conduct them on the DataFerrett website without downloading CPS data.
If you want to conduct more complex analyses with CPS, you will need to obtain CPS data. The CPS data files that you download (any of the three websites) are ASCII files, which are different from the formats used in SAS, Stata, or SPSS. Depending on what statistical software you plan to use, you will need to download and run the corresponding command files so that you can extract variables from the CPS and analyze these data.
How do I weight CPS data?
A variety of weight variables are provided for CPS monthly data and supplement data. Specifically, CPS monthly data have two key weight variables: final personal weight and final household weight. In addition, CPS March supplement data (i.e., Annual Social and Economic Supplement - ASEC) contain two main weight variables: the March Supplement person weight and the March Supplement family weight. In fall 2009, the Census Bureau released additional public use replicate weight files for the Current Population Survey’s March Supplement Data for the 2005 through 2009 collection years. The Census Bureau provides a document explaining what replicate weights are and how to use SAS, SUDAAN, and WesVar (not Stata) to incorporate these weights in the analyses: Census Replicate Weight File. However, another document from the Bureau of Census provides Stata commands on using replicate weights for American Community Survey (ACS) data (http://usa.ipums.org/usa/repwt.shtml).These Stata commands for ACS data can be modified to weight CPS data for analyses. With these replicate weight variables, researchers can generate the empirically derived standard error of the parameter estimate. It is not yet clear whether the replicate weight variables will be available for CPS March Supplement Data of 2010 and 2011.
Finally, other CPS supplemental data sets need to be weighted with different weight variables because respondents differ for different supplemental data sets. For example, special weight variables are available for researchers interested in supplement data on food security. Users of these data sets should consult the documents for each CSP supplement data set to locate appropriate weighting variables.
Where can I learn more about the CPS?
Researchers interested in using CPS can always find updates on the main CPS webpage (http://www.census.gov/cps/). In addition, reports on CPS Design and Methodology are available here: http://www.census.gov/apsd/techdoc/cps/cps-main.html. The Bureau of Labor Statistics also provides updates on CPS (http://www.bls.gov/cps). Finally,Jason Fields, a family demographer working for the Census Bureau, provides a detailed PowerPoint presentation discussing sampling design and methods employed in the SIPP. He also makes useful comparisons between the SIPP and CPS data (www.bgsu.edu/offices/mc/ncmr/ppt/ICPSR-Mar-Fam.ppt). For further help using CPS or questions about this handout please stop by the Center for Family and Demographic Research at 5 Williams Hall or email us at CFDR@bgsu.edu.