Twenty Years of Coverage: An Enhanced Current Population Survey—1989–2008

In order to appropriately evaluate state and national health reform efforts, researchers need to have a firm understanding of the historical developments concerning the rates of uninsurance and the rates of public and private coverage. This paper reports on an enhanced time series that corrects the Annual Social and Economic Supplement to the Current Population Survey (CPS) microdata for many of the changes that have occurred over the past 20 years. The CPS is the only data source that provides historical annual national and state-level estimates of the number of people of all ages in the United States without health insurance. Further, it provides details on the type of coverage that people with insurance have. The CPS will likely provide similar data into the foreseeable future. As a result of the strengths of the CPS, it is the most frequently used source of insurance estimates by national and state-level health policy analysts (Blewett et al. 2004). There are many other valuable sources for health insurance estimation, including the Medical Expenditure Panel Survey (MEPS), the National Health Interview Survey (NHIS), the Survey of Income and Program Participation (SIPP), and beginning in Fall 2009, the American Community Survey (ACS). A rich literature exists on the differences between these surveys and the pros and cons of each (Swartz 1986; Lewis, Ellwood, and Czajka 1998; Congressional Budget Office 2003; Davern et al. 2009b; State Health Access Data Assistance Center [SHADAC] 2009;). The analysis presented here is agnostic to which survey provides the most accurate estimate of coverage at any given point in time. Here, we use the CPS because it offers a relatively consistent measure over two decades on which we can improve. In this analysis, we are also agnostic about whether the CPS is capturing the true rate of uninsurance. There is substantial evidence that the CPS undercounts Medicaid coverage (Klerman et al. 2009; Davern et al. 2009a;); however, this issue is not unique to the CPS (Call et al. 2008). There is also substantial debate regarding whether the CPS captures an all-year measure of uninsurance or is closer to a point-in-time estimate (Swartz 1986; Lewis, Ellwood, and Czajka 1998; Congressional Budget Office 2003; Klerman et al. 2009;). This paper does not tackle these issues; rather, it highlights the unique ability of the CPS to provide a consistent trend controlling for known measurement, processing, and adjustment errors. Our enhanced data series makes changes to the individual records of the CPS to adjust for known consistency problems, discussed in detail below. By making changes to the individual-level microdata, it allows for the greatest utility to health policy analysts because they will be able to consistently run their specific analysis using our enhanced microdata series. Our enhanced data make changes both to the individual-level variables measuring health insurance coverage as well as to the person-level weights. Tabulated estimates using these data (i.e., predefined tables) are available from the SHADAC Data Center and the individual-level microdata are available through Integrated Public Use Microdata Series (IPUMS) CPS through the University of Minnesota's Population Center. Here, we present a summary of the results using these enhanced data examining rates of coverage over the past two decades and compare them with those available from the nonenhanced CPS.