Our findings suggest that evidence-based care for depression, when received by diverse patients in community-based settings under usual practice conditions, decreases the personal and societal burdens of depression. Improvements span clinical outcomes, quality of life, and employment status, and effects are substantively large.
From a policy perspective, it may be useful to think of our results as the average benefit that could be attained with current treatment methods if quality improvement efforts were successfully implemented for all eligible primary care depressed patients. This is a useful perspective for anticipating the consequences for public health of broad dissemination and implementation of quality improvement interventions for depression. We note that, technically, the instrumental variables method identifies the effects of treatment for patients who are likely to receive care under the intervention but not under usual care; effectiveness may be different for patients who are very likely to be treated under any practice conditions and those who are unlikely to be treated under any circumstances (Harris and Remler 1998
Our results inform public policy debates about the desirability of parity of coverage for mental health and physical health care, by underscoring the real-world effectiveness of appropriate depression care. The results regarding employment status may be particularly useful, since this outcome has not been examined in clinical trials. Strikingly, the estimated increase in employment due to treatment is very similar to the estimated decrease in employment due to depression reported elsewhere (e.g., Marcotte et al. 2000
). Our results also inform clinical practice goals by suggesting that the effectiveness of appropriate treatment as provided in community practice is comparable to that observed for standardized treatments in clinical trials, that is, remission rates greater than 70 percent for appropriate treatment and under 40 percent for no or inappropriate treatment. Thus, providers and patients no longer have to take it on faith that findings of efficacy studies for depressive disorders apply in community practice.
To put our findings in perspective, we estimate that the direct outpatient care costs of providing appropriate depression treatment over a six-month period are at most $2,134 (95 percent CI $1,898–2,371) compared with costs of $459 (95 percent CI $520–668) for patients without appropriate care. The mean difference of about $1,500 is similar to the cost of more intensive, effective quality improvement interventions for depression in primary care (Simon et al. 2001
Our study has important limitations. While we studied a diverse range of managed care practices, different findings could apply for other practices. We had moderately high dropout rates in early enrollment. Our definition of appropriate treatments is somewhat below full guideline recommendations. We rely on self-report measures of treatment; prior studies have found moder-ate to high correlation between automated pharmacy data and patients reports of antidepressant use (Katon et al. 1996
; Saunders et al. 1998
). However, in the instrumental variables framework, random error in measuring treatment does not bias the estimates of treatment effectiveness (Fuller 1987
; Bound et al. 1999
). Our dichotomous treatment measure assumes that treatment below the threshold has no effect on outcomes, and treatment above the threshold has no additional value. If these assumptions are violated, the estimated treatment effectiveness may be higher or lower than the true effect.
Our study provides a hopeful message that the burden of illness from depression can be substantially reduced through provision of appropriate care under current practice conditions in managed primary care. Policymakers and other stakeholders wishing to reduce depression's public burden should consider promoting quality improvement interventions that enable clinicians to provide appropriate care and depressed patients and their families to seek it.