1. Often these samples are gathered in the context of evaluations of specific welfare or training programs.
2. See, for example, studies by Primus et al. (1999), Cancian et al. (1999), and Rolston (1999) for a flavor of how this debate hinges on measurement issues.
3. Several earlier studies compared employment measures for low-income populations across alternative data sources, most notably the study by Greenberg and Halsey (1983) with data from the SIME/DIME Experiments. Given changes over time in such things as Unemployment Insurance coverage and response rates in surveys, we focus on the most recent studies available to maximize the relevance of our findings for the measurement of these outcomes for current and future studies.
4. Each wave of the SIPP is a longitudinal survey with between 2.5 and 4 years of data on the residents of a sample housing unit. Surveys to these respondents are asked every 4 months.
5. The NLSY79 focuses on the original respondent, but it gathers a considerable amount of information on the respondent's spouse and/or cohabiting partner.
6. Previously, earnings had to be reported in weekly amounts, and amounts over $2,000 per week were truncated. Now earnings can be reported over any interval and the data (to Bureau of Labor Statistics) are not truncated. Studies that use repeated cross-sections of the CPS that span 1994 risk misinterpreting results if they fail to account for the redesign. Polivka provides adjustment factors for earnings (at the 10th, median, and 90th percentiles) reported prior to 1994 to make the series comparable. She also shows that top-coded values that are imputed using a Pareto distribution do a good job of fitting the distribution of data that are not top coded.
7. See Bogen et al. (1997) and Bogen (1998).
8. Roemer (1999) suggests the reduction in coverage could be related to PRWORA--the March 1997 survey did not use state-specific labels for TANF benefits in 14 states that had abolished AFDC. Benefit estimates were 4.5 percentage points lower than the benchmark in states that had abolished AFDC than in states that had not. The delivery mechanism of benefits in some circumstances (for example, through employers), an enhanced sense of stigma, and caseload reductions that exacerbate recall errors may also contribute to underreporting.
9. Primus et al. adjust the CPS data proportionately to account for the decline in benefits over time, but the value of this adjustment depends on the patterns of discrepancies in the data. Unfortunately, we know little about the factors associated with the underrepresentation of program participants in the CPS or the SIPP.
10. Shroder and Martin (1996), for example, show subsidized housing (broadly defined) is badly reported on surveys, including the American Housing Survey (and presumably the SIPP). An underlying problem is that the phrase "public housing" means different things to different people, ranging from only projects to any kind of subsidized housing.
11. There are no comprehensive assessments of the quality of income and employment measurements for either the NLSY79 or the PSID. Roemer (1999) and Nelson et al. (1998) update the CPS calculations to 1996. Roemer (2000) also provides a nice discussion of adjustments that need to be made to compare aggregate SIPP and CPS totals to National Income and Product Account data.
12. Abraham et al. (1998) conclude, "There is some evidence that CPS hours worked are overreported, that this overreporting may have worsened over time. Given the paucity of data on hours worked, we view our conclusions on this subject as suggestive rather than definitive" (p. 319).
13. Moore et al. (1997) also provide a brief discussion of income data collected as part of the Gary Negative Income Tax Experiment (from the late 1960s and early 1970s). They note that the income data in this experiment, gathered through surveys of respondents, was not very reliable. In the Seattle and Denver Income Maintenance experiments, there was evidence of statistically significant underreporting of wage and salary amounts. But the magnitude of underreporting was only 2 to 4 percent, leading Halsey (1978) to conclude that they were not large enough to be important economically. The correlation between administrator records and reported values was .9, also indicating high reliability.
14. They also examine several measurement error assumptions that challenge standard practice in empirical economics.
15. We were not able to find a comparable study of trends in program participation for the SIPP. U.S. Department of Commerce, Bureau of the Census (1998) compiles summaries of an extensive, long-running research program on SIPP quality. It starts with an overview of SIPP design, and then describes sample selection, data collection, nonresponse and measurement error, data preparation, weighting, sampling error, evaluation of estimates from the 1984 to 1993 panels, and the 1996 redesign of the SIPP.
16. Despite our efforts, we have not found documentation for this particular statistic.
17. Clearly strong assumptions are needed to make this projection, but the size and industrial composition of the Illinois sample is not sharply different from national statistics. The Illinois UI system is typical of what is observed nationally, and, if anything, Midwestern states tend to have lower rates of income and payroll tax noncompliance than other states.
18. Stevens et al. (1994) is a similar study that focuses on Maryland.
19. Title II-A is the nation's employment and training program for low-income adults and out-of-school youth with significant barriers to employment.
20. Although this figure would appear to be comparable to Blakemore et al. (1996), it actually suggests a much smaller gap in coverage. This study found a 13.6-percent gap for the total workforce, while the Baj et al. (1991) study found that the corresponding gap is 13.2 percent for a JTPA sample.
21. Tabulations from the Wisconsin Department of Workforce Development (1999) suggest that as many as 16 percent (60/375) of a small sample of recent welfare recipients have missing employment episodes in UI data.
22. They do not discuss independent contractor issues that are the focus of Blakemore et al. (1996). Instead, these would be grouped into the last category.
23. All zeros in the table correspond to people without earnings in both data sets. No observations with positive earnings agreed exactly.
24. A third comparative study assessing differences in income and employment across data sources was conducted by the Rockefeller Institute of Government (Primus et al., 1999). This study summarizes (in its Table 2) six studies that compare UI data and survey data. The studies include five that we do not review in this paper and those from Kornfeld and Bloom (1999), which we do review. The results from the Rockefeller Institute study differ somewhat from the Kornfeld and Bloom results. One of two other studies finds UI earnings are lower than survey data (though one found them nearly identical), like Kornfeld and Bloom. Several other studies suggest that employment rates from surveys were significantly higher (on the order of 20 percent) than employment rates from UI data, unlike the Kornfeld and Bloom evidence. We have not assessed the quality of these other studies.
25. It also will include interest and dividend income, farm income, capital gains and losses, and gambling winnings, and indicate recipients of government transfers and Social Security benefits.
26. If one is just interested in enumerating the population (as opposed to knowing incomes associated with families and individuals within the population), IRS data appear to be comprehensive. Sailer and Weber (1999) report that the IRS population count is 95.4 percent of the Census population count. The consistency is fairly good across gender, age, and state. Unfortunately, for many of the people enumerated, the IRS does not know anything about them other than that they exist.
27. Cilke (1998) uses a CPS-IRS exact match file to examine the characteristics of people who are not required to file tax returns and actually did not file tax returns. The entire paper is presented as proportions, however, so it does not provide information on the absolute number of low-income families with earnings who fail to file.
28. For example, Bane and Ellwood (1983) estimate that 65 percent of new entrants leave the caseload in 2 years.
29. Through an interagency agreement between the California Department of Social Services (CDSS) and the state's taxing authority, the Franchise Tax Board (FTB), UI wages and wages and adjusted gross income (AGI) from tax returns were merged by the FTB. The researchers were able to specify computer runs on these merged files. Assistance units in the study could, and did, leave AFDC after they were enrolled in this study. Nonetheless, wage and income data from UI records and tax returns were available for all of the original assistance units in the CWPDP study.
30. We took great care in the analysis to make sure the comparison samples did not have changes in marital status and had a full four quarters of UI data (including zero quarters).
31. Households with low earnings are not obligated to file tax returns. For example, a married couple, is not required to file if their income is below the standard deduction and two exemptions ($12,200 in 1997), regardless of how many children they have. Hill et al. (1999) also show that most of these non filers had very low levels of UI earnings ($2,500 or less in annual covered earnings).
32. The other investigators on this project are in collaboration with David Card, Andrew Hildreth, and Michael Clune at University of California-Berkeley and Robert Schoeni at RAND.
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