This study found that better access to care has a positive effect on mental health. A USOC was directly associated with lower likelihood of screening positive for depression among community-dwelling Medicare beneficiaries. Consistent with prior studies, a USOC was also found to be associated with higher probability of having any ACU (Ettner 1996
; Sambamoorthi and McAlpine 2003
;). A simultaneous-equations model provided a better structure for estimating such effects than a single-equation model.
Our finding that USOC is associated with lower depression prevalence is consistent with a previous study on the benefits of primary care access on health outcomes and quality of depression care (Solberg et al. 2006
). To the authors' knowledge, this is the first study of a national sample of community-dwelling elderly adults to examine the effect of having a USOC on screened depression prevalence. Previous studies have found similar effect of access to care on general health status (Starfield, Shi, and Macinko 2005
) but not on mental health status specifically. In addition, this study provides evidence to support the policy changes to foster USOC in Medicare such as Medicare Advantage in that it might help address the burden of depression.
There are several potential explanations for the relationship between USOC and depression among the elderly. First, a USOC may represent an important resource for social support. Older adults residing in areas with a shortage of primary care physicians and inconvenient access to care are more likely to be rural and poor. These factors have been associated with social isolation, which in turn is a risk factor for late life depression (Prince et al. 1997
). Having a USOC may reduce social isolation and thus the risk of developing depression. This is consistent with previous research that has found that social support is associated with less depression in older adults (Brummett et al. 2000
; Moak and Agrawal 2009
;). Second, older adults rely more on health care services compared with other age groups due to increasing vulnerability (e.g., increasing disability and higher prevalence of chronic conditions). A USOC may help older adults obtain timely access to needed health care and continuity of care, which in turn result in lower risk of depression due to chronic illnesses, pain, and functional impairments. It may also help change their health behaviors to prevent stressful events. Third, people who lived in an area with a shortage of health professionals were more likely to lack a USOC. In such areas, it may take longer to get a medical appointment compared with areas without such a shortage (United States General Accounting Office [GAO] 2002
). Unmet needs have been found to be a significant predictor of depression among the elderly after controlling for income and other known correlates (Blazer, Sachs-Ericsson, and Hybels 2007
The coefficient of having any ACU was positive in the depression equation in both the single-equation model and the simultaneous-equations model. This conflicts with the assumption that health care services are beneficial for people's health. There are several potential reasons for this. On the one hand, this finding may result from persons with depression being more likely to seek care of some kind including that related to somatic symptoms. In addition, this may be due to the effect of any ACU contributing to having a USOC. Consequently, the effect of a USOC may be overestimated and the effect of health care utilization may be underestimated. On the other hand, only probability of use was considered in the present study, which assumed that having one ambulatory visit is equivalent to having many visits. This may underestimate the effect of health care utilization on depression prevalence.
Several limitations of the study must be acknowledged. First, screened depression was measured using the two-item screen based on self-reported depressive symptoms. The validity of the MCBS two-item screen as a measure of major depression has not been established. However, it is very similar in structure and in the scoring algorithm typically used to the Patient Health Questionnaire (PHQ)-2,2
a two-item version of the PHQ (Kroenke, Spitzer, and Williams 2003
). The PHQ-2 has been found to be a valid screen for major depression among the elderly (Li et al. 2007
), indicating when positive the need for further diagnostic assessment, and possibly treatment, for affective illness. The two-item screen in the MCBS data is assumed to be as good a measure as the PHQ-2. The prevalence of screened depression was estimated to be 12.9 percent in this study, which is within the range of depression prevalence reported in previous studies among community-dwelling elderly (Schulberg et al. 1998
; Lyness et al. 1999
; Blazer 2002
;). The two-item screen has high sensitivity but relatively low specificity. Even subsyndromal depression has been associated with poor health outcomes and higher service utilization, and is a risk factor for developing major depression. Thus, using the more sensitive measure has advantages. There could be recall and/or misclassification bias, which may underestimate or overestimate the effect on depression of having a USOC among the elderly. On the other hand, depression is reported by patients rather than physicians, so physician detection bias or failure to access care will not be an issue.
Second, the outcomes of interest (a USOC and screening positive for depression) were measured only once a year. Information on the trajectory of depressive symptoms was not available for the study sample, and neither was their temporal association with the USOC item specified. For example, we cannot know whether depressive symptoms are due to medical conditions or represent an autonomous affective disorder (e.g., major depressive disorder rather than major depression due to a medical condition). It is important to distinguish between depressive subgroups (type and severity) that may possess different etiological pathways and implications for treatment (Van den Berg et al. 2001
). This may limit the estimation of the effect of a USOC on depression. Third, identification (causal inference) of the triprobit model relies on either or both of the following: the parametric assumptions of the error distributions and the exclusion restrictions (instruments). While our assumptions about the instruments are plausible and the results are consistent with our expectations, there is no way to test the assumptions quantitatively. However, the single-equation model estimates suggest there may be a substantively important reverse causal relationship (i.e., depression causes visits [ACU]). That result is substantially weakened in the simultaneous equations model estimates, lending credibility to the model assumptions. The simultaneous equations results indicate the major benefit is through having a USOC.