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Interpreting Differences Between the Bureau of Labor Statistics and Decennial Census Labor Force Estimates

The Census Bureau has released Demographic Profiles from the 2000 Census. These Profile tabulations include socioeconomic and labor force data for states, metropolitan areas, counties and smaller units of geography. These data are a preview of the information that will be available later this year in the Summary File 3 (SF3) release.

Labor force estimates from the 2000 Census may differ from the official labor force data released by the Bureau of Labor Statistics (BLS) because of differences in methodology, design and data collection. The Census Bureau will conduct an analytical review after SF3 data for all states have been released. The following contains some general observations about differences between the two data series that can be made now.

Background

Every ten years, the Bureau of Census conducts a census of the population. It is a snapshot of the population for one moment in time (April 1, 2000). The main purpose of this census is to provide the population count needed for the re-apportionment of seats in the House of Representatives and determination of State legislative district boundaries.

The economic characteristics data from the 2000 Census are based on a systematic sample of approximately 17 percent of the Census households (i.e., every second, fourth, sixth, or eighth housing unit, depending on the population in the area). Some questions on the long form address economic characteristics issues, including labor force. This invites comparison with official labor force data from the BLS that are developed by the Local Area Unemployment Statistics (LAUS) program.

The Current Population Survey (CPS) has been the source of the official estimates of unemployment for the nation for more than half a century. The survey has been greatly expanded and improved over the years, but the basic concepts of employment and unemployment have remained substantially unaltered. At present, the CPS is the single, official source of the monthly statistics on unemployment for the nation and the official annual average estimate for the states. It is the main input to the estimate models that produce the official monthly labor force estimates for all states, the District of Columbia, New York City and the Los Angeles metropolitan area. Through LAUS methodology, the CPS also affects estimates for nearly 7,000 sub-state areas.

Information on unemployment has been obtained in decennial censuses since the late nineteenth century, although the current concepts were not introduced until 1940, concurrent with the beginning of the CPS. There have always been differences in measured unemployment between the CPS and the census. Prior to 1990, however, the census-based estimates of the number of unemployed had typically been lower than those from the CPS, although the gap had generally been closing over time. In 1950, the census count of unemployed persons for the nation was about 19 percent lower that the April 1950 figure from the CPS. The gap shrank to about 4 percent in 1960 and about 1.5 percent in 1970 before widening slightly to about 3 percent (lower) in 1980. Census unemployment rates were below or about the same as those from the CPS from 1950 to 1980. In 1990, for the first time, the census-based estimates of both the number of unemployed and the unemployment rate were considerably higher than the CPS figures, with the relative size of the gap being similar to that obtained in 1950, but in the opposite direction.

Conceptual and Methodological Differences Between CPS and Census

There are significant procedural and conceptual differences between the census and the CPS that are important to consider when comparing LAUS and Census estimates. The CPS is the key input to the LAUS models of the employment/population ratio and unemployment rate for the states, the District of Columbia, New York City, the Los Angeles metropolitan area and the respective balances of California and New York. Because of the LAUS estimating methodology, the CPS also has a significant impact on the labor estimates for the nearly 7,000 sub-state areas.

• Interview-controlled environment versus self enumeration

  All data from the CPS are gathered by trained field interviewers through personal visits and telephone interviews. For the most part, decennial census data are self-reported. That is, individuals fill out a questionnaire by themselves. There are generally no interviewers to clarify survey questions and probe for more accurate and detailed responses, as is the case in the CPS.

• Specific versus general survey questions

  The CPS currently uses 13 specific, detailed questions to determine ones employment status. In the census, the questions are fewer - only 6. The enhanced specificity in the CPS is designed to avoid misclassifications.

• Intensive versus limited quality control of data collection

  CPS interviewers are trained extensively before going out into the field, and proficiency checks are conducted regularly. In addition, each month, a portion of the households in the sample are reinterviewed monthly, and the results are used to control and measure the quality of the data. In the census, the extent to which the quality of the data can be controlled or evaluated is much more limited.

• Definite versus variable reference week

  The CPS questions for determining current employment status relate to a specific reference week, the week including the 12th of the month (or, in the case of a job search, the 4 weeks preceding the survey week). The census questions relate to the calendar week preceding the date that the questionnaires were completed (in the case of a job search, the 4 weeks preceding the date of reporting).

• First interview reporting bias

  In the CPS, households are in the sample for 4 consecutive months, out of the sample for the following 8 months, and then interviewed again for 4 months. There is a tendency among households surveyed for the very first time (first month in the sample) and among those surveyed after the 8-month intermission (fifth month in the sample) to report higher levels of unemployment than those who have been in the survey for several consecutive months. This phenomenon affects one-fourth of the CPS sample. In the census, virtually every household is reporting for the first time. Thus, any upward bias in unemployment associated with first interview could conceivably affect the entire census.

Comparing the State and Area unemployment Data

The BLS will be investigating the differences between the census and LAUS estimates. As the Census Bureau released decennial data for individual states, comparative tables will be issued. The comparative analysis of census and LAUS estimates will begin when all states are released.

Additional Information

For information on the decennial census, see http://www.census.gov/Press-Release/www/2002/demoprofiles.html

For more information on the CPS, see Current Population Survey Technical Paper 63, available at  http://www.census.gov/prod/2002pubs/tp63rv.pdf .

For more information on the LAUS program, see http://stats.bls.gov/lau

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