The SIPP is a large-scale survey sponsored by the Census Bureau. For the years 1990 to 1993, fresh national samples were drawn annually. Each fresh annual sample constitutes a panel. Each panel is interviewed 8-10 times; each household is interviewed every fourth month, with successive quarters of the sample interviewed in each month. A 1996 panel with interview data through March 2000 has recently been released, although the longitudinal file is not yet available. Given the resource limitations on this project, we analyzed the 1990, 1991, 1992, and 1993 SIPP panels.
In each wave, the basic questionnaire provides data on the primary jobs held during the previous four months. Questions focus on the two jobs held for the largest number of hours. For these jobs, we know earnings or wage rate, months the job was held, usual hours worked per week, industry, and receipt of health insurance coverage. These variables, together with measures of income and public assistance receipt, are the primary outcome measures for our analysis of the subsequent effects of temporary work. The SIPP supplements the basic survey in each wave with detailed topical modules that provide information including employment and welfare recipiency history. These modules are used to select comparison groups with relatively similar work histories.
Our ability to determine alternative work arrangements in the SIPP is limited to identifying workers likely to be employed by temporary help agencies. The industry categorization of the two principal jobs, which is based on a 3-digit SIC code, can be used to learn whether the worker is employed in the temporary help services industry. We categorize a person as being employed in the temporary help services industry if he/she reports that either of the two reported jobs for a given wave is in SIC 736. SIC 736 includes those working for temporary help agencies and employment agencies. The four-digit category for temporary work (which includes some leasing companies) accounts for 89 percent of employment in SIC 736; the category for employment agencies accounts for the remaining 11 percent. Because individuals self-report the SIC code, we expect relatively few persons who work at companies managed by leasing companies will report in SIC 736; they would seem more likely to report the industry in which they work.
One question that arises when using SIC 736 to define temporary help workers is how well SIC 736 identifies agency temporary workers. We examine this using the February Contingent Workers Supplement to the CPS. Using CPS data for 1995 through 1999, we find that 57-70 percent of those in SIC 736 are classified as agency temporaries based on the supplement. In addition, roughly half of those who are identified as agency temporaries in the supplement reported SIC 736 as their industry. A large share of the latter mismatch appears to result from respondents reporting the industry of the place where the temporary agency assigned them to work rather than the industry of the temporary agency. Although these findings suggest caution in using the industry code to define temporary agency workers, we believe the share of agency workers within SIC 736 is high enough that strong differentials associated with agency work will be picked up by our analysis.
Similar to the CPS, in addition to examining temporary workers as a whole, we also use the SIPP to examine the subset of workers who may be at risk of welfare recipiency. We considered definitions of at risk of welfare receipt based on public assistance receipt as well as income relative to the federal poverty level.(64) In the end, we use a definition that balances the need to have enough cases for our analysis with a low enough income cutoff such that the sample members are at significant risk of welfare receipt.
Table A.1 reports the number of spells of temporary work in the 1990-1993 panels of the SIPP. The start of each spell is sampled and used as the base period in the analysis of the effects of temporary work. These numbers include only those temporary workers with data available one year later, a necessary requirement to measure outcomes. In addition to showing sample sizes for the full sample, Table A.1 shows various possible definitions of at risk or low income, including public assistance receipt, income below 150 percent of the poverty line, and income below 200 percent of the poverty line. Given the small sample sizes, we use the broadest of the three definitions--under 200 percent of poverty--for at risk or low income. This serves to balance the need for adequately-sized samples for analysis with the need to focus on a group with sufficiently low income to be at risk of receipt of public assistance.
Appendix Table A.1
Unweighted Number of Temporary Workers in the 1990-1993 SIPP,
by Employment Status and Poverty Level in Prior Month
|Received Public Assistance in Prior Month
|Individuals below 150% of Federal Poverty Level
|Individuals below 200% of Federal Poverty Level
|Source: SIPP 1990-1993 panels, calculations by the Urban Institute.
Note: Sample sizes include all cases that are observed a year after their first month in SIC 736. Poverty figures are based on income in the month prior to employment in SIC 736.