Conclusion: Epidemiology, Etiology, & Public Health
Epidemiology places psychiatric disorders in a broad context, which is not always apparent with individual patients. This comprehensiveness is the basis of the biopsychosocial model. Goldberg suggests a version of this model that considers three kinds of factors: those that promote vulnerability (or indeed resilience), those that “release” symptoms at a particular time, and those that determine how long a particular disorder will last. Koopman adds that there is now a shift to studying complex systems that create patterns of disease. Such studies are conducted by the comprehensive monitoring of individuals as individuals and when they interact with others and their environment.
Research by Kendler and colleagues, investigating the risk factors for depression among twins, is among the first of an increasing number of epidemiologic studies based on an integrated biopsychosocial approach. Henderson extends this approach along the causal continuum in a slightly different way, noting that “the concept of populations having different frequency distributions of morbidity, not just different prevalence rates for clinical cases, carries with it the implication that some factor or factors are pushing up the over-all distribution in some groups, but not in others.” He suggests that there may be some instrumental “force” in the environment that promotes disease. According to Susser and Susser, epidemiology historically offered the paradigm of the “black box,” in which exposure was related directly to outcome, without much interest (and thus investigation) into contributing factors or pathogenesis. Moving toward a more fundamental, comprehensive, and integrative goal, these authors would suggest the alternative paradigm of “eco-epidemiology” or the study of “causal pathways at the societal level and with pathogenesis and causality at the molecular level.” Among the lessons that may be drawn then are (1) that intervention by those in health policy and practice must involve a population-based strategy rather than a singular focus on afflicted or vulnerable individuals, (2) that the web of causation is multidimensional, and (3) that theory and practice are interdependent.
Korkeila and colleagues investigated factors predicting readmission to a psychiatric hospital previous admissions, long length of stays, and a diagnosis of psychosis or personality disorder. This study was particularly important because it reconfirmed earlier work that showed that, in this era of an emphasis on community care, there may be a small group of patients who, with the current treatment strategies available, may always need frequent or longer hospital treatment.
Another important lesson was carefully drawn by Vander Stoep and Link, who emphasized the importance of using valid data in the formation of health policy. They revisited Edward Jarvis’s landmark study on the prevalence of mental illness in Massachusetts in the early 19th century. In examining social class, ethnicity, and insanity, Jarvis, wrongly interpreting his data, concluded that immigrants born in Ireland had a higher prevalence of insanity in each social stratum than did those from other ethnic groups. Jarvis then formulated elaborate theories to explain his findings, and his work had a major impact on the formation and direction of health policy of that day. A later reanalysis of the data showed that, to the contrary, the prevalence of mental illness was much lower in the foreign born than in those persons born in the United States.
Public health prevention and treatment strategies drawn from any research must be carefully and critically constructed. This will not be easy. Intervention with individuals and even populations of individuals may be both more difficult and less effective when the real “. . . target is a social entity with its own laws and dynamics.” To begin to address these issues of profound complexity and increasing topical relevance, many authors have strongly supported the reintegration of population-driven epidemiology into public health. Adding support and some urgency to this drive has been the advent of managed care, which has created information needs that only more sophisticated epidemiologic investigations can address. Questions on specific treatments for specific patient populations in specific settings; the effectiveness of various forms of health care, including management and finance strategies; and the relentless quest for ways to improve quality while simultaneously attending to related costs will all require methodologically sound investigations.
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