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CHAPTER 3. MEDIGAP 133<br />

<strong>in</strong>cludes controls for health status such as self-reported health, <strong>in</strong>dicators of medi-<br />

cal diagnoses <strong>and</strong> treatment, <strong>and</strong> widely-used measures of functional status known as<br />

Activities of Daily Liv<strong>in</strong>g (ADL) <strong>and</strong> Instrumental Activities of Daily Liv<strong>in</strong>g (IADL).<br />

Table 3.5 presents the first stage estimates of Medigap premiums on state- <strong>and</strong><br />

HRR-level costs <strong>in</strong> logs. St<strong>and</strong>ard errors are clustered at the year-by-state level<br />

because premiums vary at this level. For the purposes of our policy counterfactual<br />

analysis, the most important parameter <strong>in</strong> this table is the elasticity of premiums<br />

with respect to state-level costs. This coefficient is 0.50 to 0.60 across specifications<br />

<strong>and</strong> precisely estimated (st<strong>and</strong>ard error of less than 0.07). As discussed <strong>in</strong> Section 3.5,<br />

most of the identify<strong>in</strong>g variation comes from state-level FFS Medicare costs. With<br />

HRR costs <strong>and</strong> the other controls, the F-statistic on state-level costs is well above<br />

the critical level.<br />

Marg<strong>in</strong>al effects for the probability of Medigap choice from the mult<strong>in</strong>omial logit<br />

choice equation are presented <strong>in</strong> Table 3.6. Recall that residuals from the premium<br />

equation are <strong>in</strong>cluded as a control variable to overcome the potential endogeneity of<br />

premiums. The premium semi-elasticity of dem<strong>and</strong> is estimated at a stable 0.38 to<br />

0.48 across specifications. (The premium elasticity estimates from the l<strong>in</strong>ear proba-<br />

bility model, shown <strong>in</strong> Appendix Table 3.11, are similar, rang<strong>in</strong>g from 0.31 to 0.42.)<br />

With demographic controls, the po<strong>in</strong>t estimates are significantly negative at more<br />

than the 5 percent level. In the preferred logit specification with the full set of con-<br />

trols (specification 3), we can reject any premium elasticity outside of 0.13 to 0.82<br />

with a 95 percent confidence <strong>in</strong>terval.<br />

Males are 3 percent less likely to purchase Medigap coverage. Medigap partici-<br />

pation is 20 percent lower for blacks, <strong>in</strong>creas<strong>in</strong>g <strong>in</strong> education, but flat with respect<br />

to <strong>in</strong>come. Although we do not show it here, it should be noted that there is strong<br />

evidence that Medigap choice is <strong>in</strong>creas<strong>in</strong>g <strong>in</strong> factors the proxy for good health as<br />

well as underly<strong>in</strong>g cognitive ability (?).

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