Effect of insurance on mortality in an HIV-positive population in care

As policymakers consider expanding insurance coverage for individuals infec ted with human immunodeficiency virus (HIV), it is useful to ask if insuran ce has any affect on health outcomes and, if so, whether its magnitude has changed with recent efficacious but expensive treatments. By using data fro m a nationally representative cohort of HIV-infected (HIV+) persons receivi ng regular medical care, we estimate the impact of insurance on mortality i n this population. A naive single-equation model confirms the perverse resu lt found by others in the literature-that insurance increases the probabili ty of death for HIV+ patients. We attribute this finding to a correlation b etween unobserved health status and insurance status in the mortality equat ion for two reasons. First, the eligibility rules for Medicaid and Medicare require HIV+ patients to demonstrate a disability, almost always defined a s advanced disease, to qualify, Second, if unobserved health status is the cause of the positive correlation, then including measures of HIV+ disease as controls should mitigate the effect. Including measures of immune functi on (CD4 lymphocyte counts) reduces the effect size by approximately 50%, al though it does not change sign. To deal with this correlation, we develop a two-equation parametric model of both insurance and mortality. The effect of insurance on mortality is identified through the judicious use of state policy variables as instruments (variables related to insurance status but not mortality, except through insurance). The results from this model indic ate that insurance does have a beneficial effect on outcomes, lowering the probability of 6-month mortality by 71% at baseline and 85% at follow-up. T he larger effect at followup can be attributed to the recent introduction o f effective therapies for HIV infection, which have magnified the returns t o insurance for HIV+ patients (as measured by mortality rates).