shows the baseline characteristics of the study sample by insurance status. The insured and uninsured groups in the HRS at age 59/60 are representative of these groups in the United States. The uninsured are more likely to be in fair or poor health, to be African American or Hispanic, and to have lower education and lower income, and are less likely to work.
shows the estimated odds ratios (and their individual p-values) of the multinomial regression of health status, with the excellent/very good group being treated as the reference category. The tests of significance for key groups of variables are displayed at the bottom of the table. Here we see that the health of the uninsured is different from that of the insured both before the Medicare-eligible age and afterwards. The health status differences before and after Medicare within insurance group are significant at the p=.05 level. The difference in the rates of change pre- versus post-Medicare between the uninsured and insured is marginally statistically significant (p=.093).
Multinomial Logit Regression of Health Status in t+2
To better understand the direction of these health changes, we simulated the health trajectories depicted in . In the northwest quadrant, we see the trajectory for the excellent/very good health status. The darker lines represent the uninsured group trajectory and the lighter lines represent the insured group trajectory. The uninsured trajectory is below the insured trajectory representing their inferior health. Both lines decline with age representing deteriorating health with age. The kink at age 65 represents the change in the rate of health decline post Medicare enrollment. The dashed line represents the counterfactual that is the pre-65 trajectory, based on the pre-65 transition probabilities, extended into the post-65 ages. The divergence between the two lines for each insurance group represents the effect of Medicare on that insurance group. Here we see the increase in the likelihood of excellent/very good health with Medicare for both the uninsured and insured groups. The divergence is greater for the uninsured group. The other panels illustrate the trajectories for the other health status categories. It is notable that by age 73 the fair/poor trajectories for the insured and uninsured groups converge.
Health Status Trajectories by Insurance Group from Simulation*
As a check on the fit of our simulation we graphically plotted the raw trajectories with the trajectories from our fitted data. The lines were virtually identical providing strong evidence as to the remarkable fit of our model (see Figure S1
displays the simulated incremental effects between health trajectories based on the coefficient estimates from . In column [E] we see that for every 100 persons in the uninsured group, from age 65 to 73 joining Medicare at age 65 is associated with 4.6 more uninsured people reporting excellent or very good health, 3.0 fewer reporting good health, 3.6 fewer reporting fair or poor health, and 2.0 more as dead. Similar patterns are observed for the insured group from age 65 to 73, where joining Medicare at 65 is associated with 5.2 more insured people reporting excellent or very good health, 3.3 fewer reporting good health, 1.1 fewer reporting fair or poor health, and 0.8 fewer dead (column [F]). The magnitude of the values for the insured and uninsured groups are similar, but because of the larger sample size in the insured group the increase in excellent or very good and the decrease in good are statistically significant for the insured group and not statistically significant for the uninsured group. We note that the estimated confidence intervals account for the uncertainty generated by both sampling variation and some remaining simulation variation. If the remaining simulation variation was removed, we estimate that the confidence intervals would be at most 10–12 percent narrower, which would put the uninsured results into the range of significance.
Predicted Probabilities of Health Status Changes Simulated between Age 65 and 73
The comparisons between the insured and uninsured groups in column [G] show the uninsured with 0.6 fewer in excellent or very good health, 2.5 fewer in fair or poor health, and 2.8 more dead. These differences are not statistically significant and are small in magnitude. Given the variability in the difference-in-difference estimates as reflected by the 95 percent confidence intervals, we would have 80 percent power to detect differences of about six points between the uninsured and insured groups at the p<.05 level. This is considerable power given that this represents a narrowing of <50 percent in the baseline health disparity between the insured at uninsured based in terms of the 13 point differential probability of being in excellent or very good health.
A number of sensitivity analyses were conducted to show the robustness of this result. The details are presented in Appendix SA2 (Section B) and Tables S1 and S2
. Similar pattern of results were found when the analysis was limited to comparing those continuously uninsured in the preperiod with those continuously insured, but the death rate for the continuously uninsured is higher than the entire group of uninsured. When the uninsured are compared to those insured through Medicaid only, there is a strong relative improvement for the uninsured primarily because Medicare enrollment does little to change the health trajectory of those insured through Medicaid. This is a useful comparison because the uninsured are economically and demographically more similar to the Medicaid cohort than the privately insured cohort. There were no differences between women and men and low-income and low-wealth subgroups look remarkably similar to the overall result. The main results were not sensitive to changes in retirement status, employment status, marital status, or Social Security eligibility, which suggests that the differences within the insured and uninsured groups are unlikely to be attributed to these often contemporaneous changes at age 65. A series of other sensitivity analyses suggest that the results are insensitive to various alternative specifications.
displays the simulation for models of all of the secondary outcomes. In each case, with the notable exception of depression, there is no relative improvement in health for the previously uninsured relative to the previously insured. For depression, however, there is a 7.4 percentage point decline in active depression for the uninsured group compared with 2.3 for the insured group; this is a statistically significant difference of 5.1 percentage points that can be attributed to Medicare for the previously uninsured. On the whole, these secondary outcomes suggest that lack of an effect for the health status trajectory comparison between insurance groups is robust to other, more objective, measures of physical health.
Predicted Probabilities of Health Outcome Changes Simulated between Age 65 and 73