Moore et al. (1997) conducted a general survey of income reporting in the CPS and SIPP, and Roemer (2000) assesses trends in SIPP and CPS income reporting between 1990 and 1996.(11) A central finding in Moore et al. (1997) and Roemer (2000) is that there is underreporting of many types of income in surveys. The reasons for this and, hence, solutions in the design of effective surveys are complex. The magnitudes of CPS and SIPP underreporting for selected years are given in Tables 9-3a and 9-3b, taken from the two papers. (Note that differences may be the result of flawed benchmarks rather than flawed surveys.)
Surveys of Income Reporting in the SIPP and CPS
The understatement of certain types of income, such as interest and dividend receipts, is probably not critical for low-income populations because low-income families typically receive small amounts of income from these sources. Based on the evidence presented in Tables 9-3a and 9-3b, it appears that wages and salaries are fairly accurately reported in the CPS, although less accurately in the SIPP. But Moore et al. (1997) note that 26.2 percent (35,205,000 out of 134,135,000 total weighted cases) of the wage and salary "responses" in CPS surveys are imputed from cases where the respondent did not give an answer, replied "don't know," or refused to answer the question. They also report that 7 to 8 percent of households refuse to participate in the CPS, so imputations and imputation quality is clearly a critical element in survey quality.
The apparent accuracy of wage and salary reporting in Tables 9-3a and 9-3b does not fully resolve concerns that we have about data accuracy for low-income populations, because we do not know much about the characteristics of families that underreport their incomes. If, for example, most of the underreporting of income occurs among the disadvantaged, the findings of Moore et al. (1997) and Roemer (2000) on wage and salary reporting in the CPS and SIPP may be of little comfort. Roemer, for example, shows there are significantly more aggregate dollars reported below family income of $25,000 in the SIPP relative to the March CPS. He suggests that the SIPP does a better job than the CPS of capturing the incomes of low earners and a worse job of capturing the incomes of high earners. Learning more about the nature of underreporting would appear to be a high priority for future research.
Matching Studies of Wage and Salary Income
Roemer (2000) examines the accuracy of CPS wage and salary reports by matching CPS data to Internal Revenue Service (IRS) tax returns in selected years for the first half of the 1990s. The sample is limited to nonjoint returns and selected joint returns where each filer matches a March CPS person. The sample is restricted further to observations with no imputed wages in the CPS. He finds that in the middle of the income distribution (from $15,000 to $150,000), at least half the CPS and tax reports are within 10 percent of each other. Anywhere from 60 to 80 percent of the observations are within 15 percent of one another. Discrepancies appear much larger in the bottom and very top of the income distribution. Below $10,000 and above $150,000, at least half the observations have discrepancies exceeding 20 percent, and most are larger than that. Discrepancies are both positive and negative, though, as expected, CPS incomes tend to be larger than incomes reported on tax returns in the bottom of the income distribution, and CPS incomes tend to be smaller than incomes reported on tax returns in the top of the income distribution.
|Source of income||Indep. Estimate (billions $)||SIPP (%)||CPS (%)||Indep. Estimate (billions $)||SIPP (%)||CPS (%)|
|Wages and salaries||$1,820.1||91.4||97.3||$2,695.6||91.8||97.0|
|Rents and royalties||19.4||211.3||95.4||44.1||102.9||87.8|
|Govt. transfer income:|
|Social Security||$160.5||96.2||91.9||$ 225.5||98.3||93.0|
|Other cash welfare||2.0||135.0||120.0||2.9||86.2||80.2|
|Vets' pens. And comp.||13.9||82.0||59.7||13.8||84.1||77.5|
|Private pensions||$65.2||63.8||57.2||$ 70.2||107.1||110.8|
|Federal employee pens.||20.3||98.0||84.7||30.4||73.4||82.6|
|S&L employee pens||21.9||88.1||71.7||36.1||75.1||80.1|
|Source: These figures are adapted from Coder and Scoon-Rogers (1996).
Beyond the cited studies, there appears to be little recent work on the accuracy of the wage and salary income in the SIPP, CPS, or related national surveys.(12) The dates of the citations for American work on this topic (there also is one Canadian study) are 1958, 1970, and 1980. In each case there seemed to be a small (on the order of 5 percent) incidence of non-reporting of wage and salary income.(13) Coder (1992) compares a restricted set of SIPP households with tax data (married couples with valid Social Security numbers who file joint returns and have positive wage and salary income in either the SIPP or on tax returns) and finds a roughly 5-percent discrepancy in the existence of wage and salary income. Moore et al. (1996) examine a sample of SIPP households working for specific employers and find that respondents sometimes drop months of wage and salary receipt over a 4-month interview cycle, though virtually all accurately reported the presence of a job during the wave.
|Source of Income||Indep. Estimate (billions $)||SIPP (%)||CPS (%)||Indep.Estimate (billions $)||SIPP (%)||CPS (%)|
|Wages and salaries||$2,727.7||90.1||95.9||$3,592.3||91.0||101.9|
|Rents and royalties||45.6||113.1||85.0||76.2||82.0||58.6|
|Govt. transfer income:|
|Social Security and Railroad Retirement||$283.4||97.1||90.6||$ 332.2||87.9||91.7|
|Other cash welfare||2.9||81.9||85.6||3.4||114.0||80.5|
|Vets' pens. and comp.||14.5||83.1||73.9||17.8||72.9||89.6|
|Private pensions||$68.5||91.8||98.3||$ 98.7||98.1||93.1|
|Federal employee pens.||30.5||75.9||82.7||38.8||75.6||80.8|
|S&L employee pens.||36.9||76.8||78.7||66.0||67.8||57.3|
|Source: These figures are from Roemer (2000). The independent estimates are the mean values of the implied independent estimates from the SIPP and the CPS (from Tables -2a, 2b, 3a, and 3b in Roemer, 2000).|
Several other studies assess the quality of income and earnings measurement based on matching survey data with various types of administrative data. Bound and Krueger (1991) match CPS data from 1977 and 1978 with SSA earnings records and find essentially zero net bias in CPS income reports for those whose incomes did not exceed the SSA's earnings maximum cutoff. In fact, more than 10 percent of the CPS sample matched their Social Security reported earnings to the dollar, and 40 percent were within 2.5 percent. Second, Rodgers et al. (1993) examine wage records in the PSID for unionized men working fulltime at an hourly rate in one specific durable goods manufacturing firm in 1983 and 1987. These authors examine three common measures of earnings: earnings from the previous week, from the previous year, and "usual" earnings. They find annual earnings are reported fairly reliably, but this is less true for the other two measures. They also find for each measure that there is a tendency for workers with lower than average earnings to overreport and for workers with higher than average earnings to underreport.(14)
Studies of Program Participation and Transfer Income
The previous discussion focused on income reporting. There are also several studies of transfer program reporting in surveys, though the cited studies are old (dates for the citations are 1940, 1962, 1969, 1969, 1971, 1975, 1978, 1980, and 1984). These are not "complete" design studies, in that they typically focus on a sample of recipients and examine whether or not they report benefits. Complete designs also would look at nonrecipients and see if they falsely report receipt. More recent studies do the latter. Most, but not all, of these studies find fairly substantial underreporting of transfer program receipt.
Marquis and Moore (1990), using two waves of the 1994 SIPP panel, did a comprehensive study of the accuracy of reporting of transfer program participation. They discuss evidence of substantial underreporting of program participation among true program participants, on the order of 50 percent for Workers' Compensation and AFDC, 39 percent for UI and 23 percent for food stamps and Supplemental Security Income. Overall participation rates for transfer programs, however, were quite close to what would be expected from administrative controls.
Subsequent work by Moore et al. (1996) on a sample of households from Milwaukee found smaller underreporting among true recipients, and found that most error, when it exists, is due to participants' failures to report the sources of income, rather than a failure to report all months of participation.
Bollinger and David (2001) give a detailed examination to food stamp underreporting in the 1984 SIPP panel. They find that the high rate of underreporting for food stamps arises in part from failures to locate the person legally certified within the household. About half of the underreports within a household were offset by an overreport from another household member. The net effect was underreporting of food stamps receipt of 12 to 13 percent in the 1984 SIPP panel. Bollinger and David also (2001) document the important point that nonresponse and false answers are correlated across survey waves in the SIPP.
Finally, Yen and Nelson (1996) examine survey and administrative records from Washington state and find that 93 percent of the nearly 49,000 person-months are reported correctly, and net overreports roughly equal net underreports.
Assessment of Income and Transfer Program Reporting in National Surveys
Moore et al. (1997:12) conclude their survey of what is known about income measurement in surveys by stating that:
Wage and salary income response bias estimates from a wide variety of studies are generally small and without consistent sign, and indicators of unreliability (random error) are quite low. Bias estimates for transfer income amount reporting vary in magnitude but are generally negative, indicating underreporting, and random error also is an important problem.
They conclude, "in general we find that the additional data continue to support the conclusion of very little bias in survey reports of wage and salary income, and little random error as well." They conclude that studies that match administrative records of transfer programs and survey data "suggest a general tendency for transfer program income to be at least modestly--and in some instances substantially--under reported" (p. 16).
Based on our review of available assessments of income and employment measurement in national surveys, we think the above quotation is still correct. The CPS, SIPP, NLS, and PSID surveys provide:
- Valuable information on the behavior of the low-income population (and many other issues). They have national samples, and broad and fairly accurate measures of income, and their focus on families as the unit of analysis and their ease of access greatly enhance their value.
- The value of these data sets for evaluating welfare reform is severely limited, however. With the devolution of responsibility for TANF, the CPS and SIPP sampling frames and sample sizes mean that, at best, they can be only supplementary data sources for understanding the effects of welfare reform at the state and local levels. The apparent decline in program coverage in the CPS is also worrisome.(15)
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