Winterbottom et al. (1995) combined data from the 1991, 1992, and 1993 March CPS surveys to obtain state-level estimates of the health insurance status of individuals. Because CPS households are interviewed for two consecutive years and Winterbottom et al. only wanted to include each household once, they included all the observations from the 1993 CPS plus approximately half of the observations from the 1991 and 1992 surveys. Thus, combining three years of CPS data doubles the sample size, which reduces the sampling variance.(25) Winterbottom et al. then used The Urban Institute's TRIM2 model to adjust for underreporting of Medicaid.
Winterbottom et al. found that the rate of uninsured among children age 0 to 17 varied by state and region. For example, in the West South Central region -- the region with the highest rate of uninsurance -- 18.5 percent of children were uninsured.(26) In contrast, in the East North Central region -- the region with the lowest rate of uninsurance -- 6.8 percent of children were uninsured.(27) Winterbottom et al. pointed out that uninsurance rates vary by region and state for a number of reasons, including the rate of employer-sponsored insurance coverage and the rate of Medicaid coverage. Winterbottom et al. used the following example of the uninsurance rates of all persons age 0 to 64 to illustrate their point:
"The Middle Atlantic region has the lowest rate of employer coverage among its poverty population -- only 11.5 percent have employer-sponsored coverage -- significantly lower than the 15.8 percent coverage in the Mountain states. However, because the Middle Atlantic region has a high rate of Medicaid enrollment in the poverty population -- 53 percent of the poor get their primary coverage through the program -- its uninsured rate of 25.1 percent is not the highest. The Mountain States, with greater employer coverage among the poor, have a higher uninsured rate (32.6 percent) than the Middle Atlantic region because Medicaid covers fewer of the poor in the Mountain States region (40 percent)."