Comorbidity indices: a call for the integration of physical and mental health.

Comorbidity indices are commonly used in health services research as a measure of, or as a control for, the severity of a person's medical state. Currently, there is not a comorbidity index for mental health diagnoses, despite the fact that almost half of Americans have a diagnosable mental health condition at least once in their lifetime. This commentary calls for the integration of mental and behavioral health in comorbidity indices to appropriately account for the role of mental health in overall morbidity and mortality.