and colleagues found no evidence for discontinuities in employment status, marital status, geographic location, or family income that might explain discontinuities in general health, suggesting these reduced disparities were due to increases in coverage after age 65 (Card et al., 2004).
In a related study, Decker and Remler used Canadian adults as international controls (Decker and Remler, 2004). Age profiles of general health status were constructed from National Health Interview Survey data for U.S. adults and from the National Population Health Survey for Canadian adults ages 55 to 74 and compared by income, country, and age (65 or older vs. under 65) in a quasi-experimental approach. Among the near-elderly age group, low-income adults in the United States were 15 percentage points more likely than high-income adults to be in fair or poor health, compared to an 8 percent absolute difference between low- and high-income adults in Canada. Among adults age 65 or older, this 7 percent international difference was reduced to 3 percent, suggesting that near-universal Medicare coverage reduced the excess risk of fair or poor health among low-income adults by 4 percent—or equivalently, that not having insurance explained more than half of the health disparity between low-income and high-income nonelderly adults in the United States.
In these studies of cross-sectional data, effects of Medicare coverage on other measures of health were not assessed, and uninsured adults, particularly those with specific conditions who might benefit most from coverage, could not be longitudinally followed as they became eligible for Medicare. Several subsequent studies used longitudinal data from the HRS to assess the effects of gaining Medicare coverage on the health of previously uninsured adults.
In an observational study, Baker and colleagues found that adults without health insurance for 1 to 2 years prior to age 65 were more likely to report a major decline in general health or a new functional limitation in their first interview after age 65 (Baker et al., 2006a). In subsequent interviews, after at least 2 years of Medicare eligibility, previously uninsured adults no longer reported significantly higher rates of these health declines.
In a quasi-experimental study, Polsky and colleagues used more recent data from the HRS to follow participants longer after age 65 and compared trajectories in self-reported general health between insured and uninsured near-elderly adults before and after age eligibility for Medicare (Polsky et al., 2006). Health declines became less frequent after age 65 for previously uninsured adults, such that the proportion of these adults reporting excellent or very good health after age 65 was nearly 8 percent higher than expected based on their trajectory before age 65. However, previously insured adults also reported a significant improvement in their health trajectory after age 65. This change in trajectory was slightly smaller, suggesting a net positive health effect for previously uninsured adults attributable to