Effect of Usual Source of Care on Depression among Medicare Beneficiaries: An Application of a Simultaneous-Equations Model

Little research has been conducted on the relationship between access to care and depression prevalence among the elderly. The objective of the present study is to investigate the effect of having a usual source of care (USOC) on depressive symptom prevalence among Medicare beneficiaries. This question is important because (1) depression is prevalent among the elderly; (2) detection and treatment of depression are critical for its prognosis; (3) USOC, a structural measure of access to care, often serves as entry to the medical and mental health care systems; and (4) there are disparities in mental health and having a USOC has been found to decrease inequalities in health. Studies are needed to examine whether having a USOC also helps decrease inequalities in mental health. Depression is a major public health problem among people age 65 and older. The prevalence of major depression among the elderly in primary care settings is 6–9 percent (Schulberg et al. 1998; Lyness et al. 1999;), and as high as 8–16 percent for clinically significant depressive symptoms (Blazer 2002). Major depression has been found to be associated with morbidity, mortality, compromised quality of life, and higher health care expenditures (Wells et al. 1989; Broadhead et al. 1990; Simon, Vonkorff, and Barlow 1995; Unutzer et al. 1997;). Depression is projected to be second only to ischemic heart disease as the leading cause of disability adjusted life years by 2020 (Murray and Lopez 1997). Early identification and proper treatment significantly decrease the negative impact of depression in most patients (Coulehan et al. 1997). Access is a prerequisite for receiving health care that affects mental health. Having a USOC can be classified as a structural measure of access to care (Sox et al. 1998), which has been found to be associated with higher health care utilization (including preventive, primary care, and specialty services), better health outcomes, and reduced disparities for health care utilization and health (Ettner 1999; Corbie-Smith et al. 2002; De Maeseneer, De Prins, and Gosset 2003; DeVoe et al. 2003; Starfield and Shi 2004; Starfield, Shi, and Macinko 2005;). Most previous studies about the relationship between access to care and health status have focused on general and/or physical health. No study has examined the effect of access to care on mental health status among the elderly. The IMPACT, PROSPECT, and PRISM-E trials focused on care management for elderly with clinical depression in primary care settings (Unutzer et al. 2001; Levkoff et al. 2004; Alexopoulos et al. 2005;). In addition, most previous studies failed to control for the unmeasured selection bias (potential heterogeneity-generated endogeneity) among access to care, health care use, and health status, resulting in potentially biased findings. The purpose of the present study is to examine the effect of having a USOC on depressive symptoms among Medicare beneficiaries controlling for potential endogeneity. Our hypothesis is that having a USOC is associated with lower depressive symptoms prevalence among the elderly.