The Scope of Inquiry in Psychiatric Epidemiology
“Epidemiology” is derived from the Greek words epidemos, meaning “among the people”, and is defined as the study of “thepatterns of disease occurrence in human populations and of the factors that influence these patterns” (MacMahon and Pugh, 1970). Because the ultimate goal of epidemiological research is to understand the cause of disease and prevent its occurrence, epidemiology is the backbone of public health.
Important advances have been made in psychiatric epi-demiology, largely since World War II. To make such advances, investigators have had to overcome formidable problems that are unique to the study of psychiatric disorders. Foremost among their achievements has been the development of the ability to define mental disorders reliably and efficiently. This accomplishment has in turn allowed investigators to conduct descriptive analyses that have yielded much-needed estimates of the incidence, prevalence, age at onset, and frequency of recurrence of mental disorders.
The ability to accurately categorize cases and noncases has also been essential for allowing psychiatric epidemiologists to progress from simple descriptive work establishing rates to ana-lytical research aimed at identifying risk factors, as well as bio-logical and psychosocial variables that modify the effects of these risk factors. Examples of promising areas in which there has been significant research activity recently include investigations of the genetic bases for psychiatric disorders (Risch and Merikangas, 1990) and the modification of risk by environmental exposures, especially in the prenatal period (Neugebauer et al., 1999).
Whereas traditional epidemiology has largely been con-cerned with the occurrence and causes of disease, clinical epide-miology has emerged as a closely related discipline which seeks to identify the occurrence and determinants of clinical outcomes from illnesses (Weiss, 1985; Sackett et al., 1985). Clinical epide-miologic studies employ the same principles and methods of pop-ulation-based epidemiology, but are usually conducted among clinical samples. Recent clinical epidemiologic investigations such as the NIMH Collaborative Program on the Psychobiology of Depression (CPPD) and the Harvard–Brown Anxiety Research Program have provided important information on prognostic fac-tors associated with the natural history of psychiatric disorders (Judd et al., 1998; Rogers et al., 1999). Other examples include two countywide longitudinal studies of first-admission psychosis (Beiser et al., 1989; Bromet et al., 1992), which included patients from all facilities in the respective geographical regions, or a follow-up study of first-episode psychotic patients admitted to the McLean Hospital in Belmont, Massachusetts (Tohen et al., 1992). Psychopharmacoepidemiology has been an especially fast growing component of clinical epidemiologic inquiry (Wang et al., 2002b), in part because psychotropic medications are now widely used in both general medical and psychiatric populations. Many psychopharmacoepidemiologic studies have consisted of descriptions of the patterns and predictors of psychiatric medica-tion use (Olfson et al., 2002; Wang et al., 2000) as well as inves-tigations of unanticipated hazards from psychiatric medications (Wang et al., 2001a, 2001b, 2001c, 2002a, 2002c).
Clinical epidemiologic research has also begun to evaluate the economic costs associated with mental disorders, both the direct costs for provision of mental health services as well as the indirect costs to society, secondary to the disability caused dis-orders. The WHO Global Burden of Disease (GBD) study (Mur-ray and Lopez, 1996) identified mental disorders as among the most costly diseases in the world. For example, major depression was the single most burdensome disease in the world among in-dividuals under 45 years of age. Another closely related area of inquiry is that of mental health services research. This discipline investigates the patterns of utilization of mental health services, unmet needs for treatment, barriers to help seeking, the appropri-ateness and quality of treatments, and premature dropout from treatment (Kessler et al., 2001; Wang et al., 2000, 2002; Edlund et al., 2002).
The accumulation of information on risk factors for men-tal disorders, their outcomes, and treatment has in turn led to another important line of inquiry in psychiatric epidemiology, namely, interventional research. In addition to efficacy trials of psychiatric treatments conducted under rigorously controlled conditions (Tohen et al., 2000, 2002), recent experimental stud-ies have also begun to include effectiveness trials of “real-world” treatment strategies (Katon et al., 1995, 1996; Simon et al., 2000; Wells et al., 2000). Finally, the proliferation of effective but costly interventions, coupled with growing constraints on health care budgets, have also made it imperative to study not only the effectiveness of interventions but also their cost-effectiveness and cost-benefits. For this reason, economic analyses now fre-quently accompany efficacy and effectiveness trials of interven-tions (Schoenbaum et al., 2001).