How does the persistence of depression influence the continuity and type of health insurance and coverage limits on mental health therapy?

AIM OF THE STUDY: To determine the structural effect of the persistence of depression on continuity and type of health insurance and coverage limits on mental health therapy.

METHODS: Data came from the Partners in Care study (PIC), a randomized controlled trial examining the effect of quality improvement (QI) programs involving medication or psychotherapy on the outcomes of initially depressed patients in seven managed care settings. The sample included approximately 945 adult patients under the age of 63 years who were primarily depressed and insured at baseline. Single-equation multivariate probit regressions were estimated to determine the association of depression burden days aggregated over the 6 to 24-month period post-baseline with the following dichotomous outcomes: continuous health insurance over 6 to 24 months; continuous private health insurance over 6 to 24 months; any public health insurance over 6 to 24 months; and reporting no insurance limits on mental health therapy coverage at 24 months. Other control variables included baseline insurance status, age, sex, race, marital status, education, income, assets, fixed site effects, and (in sensitivity analyses) number of medical comorbidities, alcohol use and drug use. To address the possibility of endogeneity bias in the relationship between depression and insurance, consistent estimates were derived from instrumental variables (IV) probit regressions and the endogeneity of depression burden days was tested. Potential instruments included the random assignment to intervention and control groups in the PIC study, type of depression at baseline, and baseline Mental Component Summary (MCS) score from the Short Form-12 (SF-12). In sensitivity analyses, data pooled (rather than aggregated) across waves were used to estimate probit and IV probit regressions, using Generalized Estimating Equations methods to adjust for within-person correlation of the error terms.

RESULTS: Evidence was found that depression burden days were exogenous to all of the health insurance outcomes except for coverage limits on mental health therapy. Based on the appropriate estimates (single-equation if exogenous, IV if endogenous), depression burden days appeared to increase the probability of having any public health insurance coverage and decrease the probability of having no coverage limits on mental health therapy. However, these effects were small in magnitude.

CONCLUSIONS: Reverse causality may be more of a concern when examining the influence of depression on mental health care coverage than on health insurance in general. Consistent with the government's historical role in financing mental health services, patients whose depression persisted to a greater extent were slightly more likely to have some public health insurance during an 18-month follow-up period. Furthermore, they were slightly more likely to have limits on mental health therapy coverage, suggesting that insurers may be more likely to control access at the level of the benefits structure than at the level of insurance coverage per se. Future analyses should examine the mediating factors in the relationship between depression and limits on mental health therapy coverage, e.g., diminished employment opportunities with large companies that offer more generous benefits.