Guidelines for evaluating prevalence studies

As stated in the first issue of Evidence-Based Mental Health, we are planning to widen the scope of the journal to include studies answering additional types of clinical questions. One of our first priorities has been to develop criteria for studies providing information about the prevalence of psychiatric disorders, both in the population and in specific clinical settings. We invited the following editorial from Dr Michael Boyle to highlight the key methodological issues involved in the critical appraisal of prevalence studies. The next stage is to develop valid and reliable criteria for selecting prevalence studies for inclusion in the journal. We welcome our readers contribution to this process. You are a geriatric psychiatrist providing consultation and care to elderly residents living in several nursing homes. The previous 3 patients referred to you have met criteria for depression, and you are beginning to wonder if the prevalence of this disorder is high enough to warrant screening. Alternatively, you are a child youth worker on a clinical service for disruptive behaviour disorders. It seems that all of the children being treated by the team come from economically disadvantaged families. Rather than treating these children on a case by case basis, the team has discussed developing an experimental community initiative in a low income area of the city. You are beginning to wonder if the prevalence of disruptive behaviour disorders is high enough in poor areas to justify such a programme. Prevalence studies of psychiatric disorder take a sample of respondents to estimate the frequency and distribution of these conditions in larger groups. All of these studies involve sampling, cross sectional assessments of disorder, the collection of ancillary information, and data analysis. Interest in prevalence may extend from a particular clinical setting (a narrow focus) to an entire nation (a broad focus). In …