摘要：Objectives . We examined the prevalence of psychiatric illness among 3 homeless populations in St. Louis, Mo, in approximately 1980, 1990, and 2000. The 3 studies were conducted with the same systemic research methodology. Methods . We compared selected demographics and lifetime substance abuse and dependence and other mental illness among the 3 populations. Results . Among the homeless populations we studied, the prevalence of mood and substance use disorders dramatically increased, and the number of minorities within these populations has increased. Conclusions . The prevalence of psychiatric illness, including substance abuse and dependence, is not static in the homeless population. Service systems need to be aware of potential prevalence changes and the impact of these changes on service needs. Addressing the public health concerns of the homeless population is a major challenge for service providers and policymakers. This population suffers from multiple risk factors, including disproportionately high rates of mental illness and substance use and abuse. Understanding the risk factors and their changing roles is essential for the development of effective policies and programs that address these concerns. Comparing homeless populations across studies and over time has been impeded by methodological difficulties, 1, 2 including inconsistent definitions of homelessness, varied sampling strategies and locations, and disparate measurement instruments. Differences in population prevalence estimates of homelessness vary by tens of millions because of sampling: low estimates are generated from samples of current homeless-shelter users only (current prevalence, literal homelessness), 3 and high estimates are generated from samples of individuals with any lifetime episode of unstable housing (lifetime prevalence, marginal housing). 4 This situation complicates efforts to weigh risk factors for homelessness, such as mental illness or substance abuse, across populations and over time. Despite controls for sampling variation, only questionable reliability has emerged in comparisons of standardized and clinician-based estimates of risk. 5 Reasonably reliable cross-sectional prevalence estimates and risk factors have emerged from adequately designed population studies over the last decade, 2, 6– 16 but the effects of time have not been adequately tested in these studies. The homeless population is always described at a discrete time point, which conceptualizes homelessness as a static phenomenon. Changes in the demographics of the homeless population over time may have critical implications for service and public health policy implementation. Housing and labor markets, 17– 21 erosion of public benefits, 21 and deinstitutionalization 19, 21, 22 all have been identified as risk factors for homelessness. Changes in these forces over time may shape the evolving complexion of the homeless population and may contribute to the level of mental illness or substance abuse within it. A substantial body of research has shown that economics and federal and state policies powerfully affect risks for homelessness. 23 Longitudinal data on the homeless population are generally unavailable. Therefore, the evolving dynamics of this population’s demographics are most readily examined by comparing available data from different time periods. Although longitudinal studies represent the gold standard for examining changes in prevalence of risk factors in the homeless population, separate studies that employ similar sampling methods and instrumentation conducted at different times offer an alternative approach. This rationale forms the basis of our study, which capitalizes on population data from 3 studies conducted in St Louis, Mo, at 3 different time points approximately a decade apart. These 3 studies utilized the same methodology with systematic sampling and structured psychiatric interviews, which yielded full psychiatric diagnoses that met American Psychiatric Association (APA) criteria. The purpose of our study is to compare selected demographics and relative prevalence of lifetime psychiatric and substance abuse and dependence diagnoses among 3 homeless populations that were systematically assessed by structured interviews in approximately 1980, 1990, and 2000.
