Table 2.
Summary of Principal Study Findings on Effects of Medicare Coverage on Health Measures for Previously Uninsured Adults*
|
McWilliams et al. (2007a) |
Polsky et al. (2009) |
||||||
|---|---|---|---|---|---|---|---|
| Differential Change in Trend after Age 65† (p Value) |
Differential Change in Probability of Health State by Age 73‡ (95% CI) |
||||||
| Health Measure | Entire Study Cohort | Cardiovascular Disease or Diabetes before 65 | No Cardiovascular Disease or Diabetes before 65 | Best Health State | Intermediate Health State | Worst Health State | Dead |
| General health | 0.00 | 0.01 | −0.01 | −0.6 | 0.3 | −2.5 | 2.8 |
| (0.90) | (0.64) | (0.49) | (−4.8, 3.4) | (−3.8, 4.1) | (−7.4, 2.3) | (−4.0, 10.0) | |
| Change in general health | 0.02 | 0.02 | 0.01 | 0.4 | −0.4 | −1.9 | 1.9 |
| (0.01) | (0.03) | (0.17) | (−1.8, 1.8) | (−6.4, 5.5) | (−5.2, 2.9) | (−6.1, 7.9) | |
| Mobility | 0.03 | 0.04 | 0.01 | −0.9 | 2.1 | −3.9 | 2.7 |
| (0.06) | (0.05) | (0.74) | (−7.6, 2.7) | (−0.6, 5.9) | (−7.2, 2.0) | (−3.8, 9.3) | |
| Agility | 0.05 | 0.08 | 0.01 | 0.3 | 0.1 | −2.7 | 2.3 |
| (0.004) | (0.003) | (0.51) | (−4.4, 3.9) | (−2.3, 3.6) | (−7.5, 2.9) | (−4.4, 8.2) | |
| Pain | 0.02 | 0.02 | 0.00 | 1.7 | −1.8 | −1.9 | 2.0 |
| (0.18) | (0.08) | (0.96) | (−5.0, 7.2) | (−2.8, 0.6) | (−5.0, 2.5) | (−4.3, 8.2) | |
| Depressive symptoms | 0.06 | 0.04 | 0.08 | 1.5 | 1.1 | −5.1 | 2.5 |
| (0.01) | (0.32) | (0.002) | (−4.3, 4.7) | (−1.2, 6.1) | (−9.3, −1.3) | (−4.5, 9.2) | |
| 0.20 | 0.26 | 0.10 | |||||
| Summary health measure | (0.002) | (0.006) | (0.17) | — | — | — | — |
| Adverse cardiovascular outcomes | −0.009 | −0.015 | −0.002 | ||||
| (0.006) | (0.02) | (0.52) | — | — | — | — | |
Estimates in bold are statistically significant, as indicated by p values ≤.05 or confidence intervals that do not include zero. It is notable that Polsky and colleagues focused their principal and sensitivity analyses on the only component health measure, general health status, for which we found no effect of Medicare coverage for previously uninsured adults. Both studies found significant differential improvements of Medicare coverage on depressive symptoms for previously uninsured adults.
Differential changes in health trends were estimated by fitting linear spline regression models of component or summary health scores as a function of insurance coverage before age 65, age in years, number of years over age 65, and interactions between insurance coverage and these two age variables. Thus, previously insured and previously uninsured adults were allowed to have different trends before age 65 and different changes in trends after age 65. Positive differential changes in trends for previously uninsured adults indicate relative improvements in health associated with gaining Medicare coverage for all component and summary health measures except adverse cardiovascular outcomes, for which negative differential changes indicate improvements. All estimates were adjusted for the complex design of the survey, nonresponse due to death, nonresponse due to dropout, and baseline demographic and socioeconomic characteristics.
Differential changes in predicted probabilities of particular health states were simulated from a transition state model, for which transition probabilities were estimated by fitting multinomial regression models for each component health measure. These multinomial regression models estimated the log odds of being in particular health states at time t+2 years relative to a reference state as a function of: health states at time t; insurance coverage before age 65; an indicator of age over 65; an interaction between insurance coverage and this age indicator; interactions between insurance coverage and health states at time t; interactions between the age indicator and health states at time t; three-way interactions between insurance coverage, health states at time t, and the age indicator; age; age squared; sex; race; education; and Census region. Thus, previously insured and previously uninsured adults were allowed to have different rates of transition between health states before age 65 and different changes in these rates after age 65, similar to the linear spline model estimated by McWilliams and colleagues. Accordingly, relative risks of transitioning to death for previously uninsured adults were held constant before age 65 and allowed to change once after age 65. Simulated changes reported in the table are the estimated effects of Medicare coverage on previously uninsured adults' probabilities of being in particular health states by age 73. Positive changes indicate beneficial effects of Medicare coverage for better health states, while negative changes indicate beneficial effects for worse health states.