Unlike some previous studies (Rost et al. 2000
; Furedi et al. 2003
; Tai-Seale, McGuire, and Zhang 2007
;), we found no evidence for the crowd-out hypothesis associated with initiation of mental health care use after the first, second, and third PCP visits. It seems undeniable that dealing with other conditions takes time within a primary care visit. Future research examining the actual content of provider–patient interaction within a visit is necessary to make progress on the question of the behavior of patients and physicians around information exchange and problem presentation.
No detection of a crowd-out effect may also be due to limitations in our data. Our data could not identify whether a mental health care referral was made at the PCP visit, possibly a better indicator of whether crowd-out occurred. We thus cannot be sure whether the patient's failure to initiate mental health care was due to a lack of referral or the patients' failure to act upon the clinician's advice. Initiation of mental health treatment is ultimately a patient decision and action, and an interaction among comorbidity and race/ethnicity around following up on a referral might diminish the crowd-out effect. Another limitation of the MEPS data is that, except for prescription drug start dates, only the round of each prescription drug fill is known and dates had to be imputed. However, we remain confident in the direction of our findings because we expect that errors in prescription fill date imputations will not differ by comorbidity status or racial/ethnic group, and because findings from sensitivity analyses comparing mental health care initiation for 60 days post PCP visit were similar to 30 days post PCP visits. Additionally, understanding racial/ethnic differences in rates of chronic health conditions such as cancer and cardiovascular care is complicated by the fact that racial/ethnic minorities are more likely to be diagnosed at later, more aggressive stages of these diseases. Relying upon self-report of clinician diagnosis as opposed to medical examination data may lead to the misclassification of a number of blacks and Latinos as having no comorbidities. It is unclear in what direction this biases our results but improved diagnostic data would help to improve our understanding of whether blacks and Latinos experience crowd-out differently from whites.
We found evidence that the increased exposure to physicians due to the care needed to treat comorbid physical health conditions improved the likelihood of initiation of mental health care for those in need for care. This is consistent with two previous studies that showed positive associations between physical illness and mental health care treatment (Sambamoorthi et al. 2006
; Teh et al. 2008
). One clinical implication is that improving the rates at which individuals keep their check-up appointments will not only benefit the treatment of the chronic physical illness but also improve the ability of providers to recognize and treat or refer to treatment for comorbid mental illness. Another possible implication is that increasing the number or length of visits may be a straightforward and relatively inexpensive way of improving recognition of need for mental health care for racial/ethnic minorities with comorbidities.
Our findings suggest three potential pathways by which disparities in access to mental health may arise and be addressed. First, greater exposure to the health care system for racial/ethnic minorities with comorbidities improves initiation of mental health care. Given these results, intensive follow-up care and disease management are likely, not only to reduce disparities in chronic disease outcomes (Hypertension Detection and Follow-Up Study 1979
; Goldman and Smith 2002
; Franks and Fiscella 2008
;) but also to have favorable spillover effects into initiation of needed mental health care treatment. Second, disparities may arise simply because whites have higher rates of a number of comorbid conditions than Latinos and African Americans which translate to their greater need for and use of services. Third, the coefficients measuring the interaction between comorbidities and racial/ethnic group were negative (though not significant) in the first PCP visit and in the exposure analyses. This result provides marginal evidence that blacks and Latinos were less likely to benefit from greater exposure to the health care system than whites, perhaps because of racial/ethnic minority patients' greater difficulty in communicating with their providers (Roter et al. 1997
; Van Ryn 2002
; Johnson et al. 2004
Our exposure conclusions are predicated upon the validity of the use of number of preperiod visits as an instrument of number of postperiod visits. We have demonstrated evidence of the validity of two main assumptions of IV analysis: that preperiod visits have a nonzero association
with postperiod visits and the exclusion restriction
—that preperiod PCP visits are related to the outcome only through their effect on postperiod PCP visits. Instrumental variable analysis rests on other assumptions as well (Landrum and Ayanian 2001
). Among these are that we assume assignment of the instrument is ignorable
, meaning that survey respondents that differ in number of preperiod PCP visits are similar on observed and unobserved characteristics as if number of PCP visits was randomly assigned. We also assume that the number of postperiod visits for one subject does not affect the likelihood of initial mental health treatment of another subject. Potential correlation of our instrument with unobserved variables is a threat to the validity of our interpretations.
How the investigator chooses to treat comorbidities matters when measuring mental health care disparities. Black–white disparities in initiation of mental health care services increased and Latino–white disparities decreased when racial/ethnic differences in comorbidities were adjusted for in the calculation of disparity. The choice of whether to adjust or not in the context of the IOM definition depends on whether comorbidity is considered as a need variable or a systems variable. We should adjust for physical illness if we are confident that it affects use only through need for care. We should allow differences due to comorbid physical illness if we think differences in exposure for individuals with comorbidities are driven by factors within the health care system.
Disparities in health care use are only a concern when the services are needed. The “white standard” may include some unnecessary as well as needed services. By confining our analysis to persons with low self-assessed mental health status, we can be reasonably sure that initiation of some mental health care is potentially useful among our study group.
Other variables, in addition to comorbidity, have ambiguous interpretation in models of health care use for purposes of disparities measurement, such as insurance, marital or employment status. Insurance status, for example, can be correlated with unmeasured health status. Minorities and whites differ on these characteristics, and these measures tend to have large effects on rates of use. As in the case of comorbidities, careful examination of the role of these factors (Are they correlated with need? Are they indicators of social support or time costs?) would pay dividends in terms of clarifying the magnitude of disparities as well as the forces responsible for them.