A Systematic Review of the Prevalence of Schizophrenia

Background: Understanding the prevalence of schizophrenia has important implications for both health service planning and risk factor epidemiology. The aims of this review are to systematically identify and collate studies describing the prevalence of schizophrenia, to summarize the findings of these studies, and to explore selected factors that may influence prevalence estimates. Methods and Findings: Studies with original data related to the prevalence of schizophrenia (published 1965–2002) were identified via searching electronic databases, reviewing citations, and writing to authors. These studies were divided into “core” studies, “migrant” studies, and studies based on “other special groups.” Between- and within-study filters were applied in order to identify discrete prevalence estimates. Cumulative plots of prevalence estimates were made and the distributions described when the underlying estimates were sorted according to prevalence type (point, period, lifetime, and lifetime morbid risk). Based on combined prevalence estimates, the influence of selected key variables was examined (sex, urbanicity, migrant status, country economic index, and study quality). Conclusions: There is a wealth of data about the prevalence of schizophrenia. These gradients, and the variability found in prevalence estimate distributions, can provide direction for future hypothesis-driven research. Analysis of 188 studies published between 1965 to 2002 yields no difference between men and women and suggests that current text-book estimates for lifetime morbid risk are too high. Background.: Schizophrenia is a very serious mental illness and a major contributor to the global burden of disease. The topic of this study is the question of how common schizophrenia is among different groups and in different countries around the world. “Prevalence” means the number of people who have the disease at a particular time. The study itself is a so-called systematic review, which means the researchers used prespecified methods for finding individual studies and for extracting and summarizing the data from these individual studies in as objective a way as possible. Why Was This Study Done?: Health care planning is based on prevalence estimates, and as a result, many studies on schizophrenia prevalence have been done by researchers around the world. The authors decided to do a systematic review of these studies to come up with a scientifically sound view of the big picture. What Did the Researchers Do?: They looked at a total of 1,721 estimates of the prevalence of schizophrenia from 188 studies and covering 46 countries. They then calculated median prevalence estimates (that is, the middle value of all estimates) over a variety of time periods (see below). What Did They Find?: The take-home message from their study is that about seven to eight individuals out of 1,000 will be affected by schizophrenia. To be more precise, the researchers found the following median estimates for the prevalence of schizophrenia: 4.6 out of 1,000 people have the disease at a specific time point; 3.3 per 1,000 have the disease within a surveillance period one to 12 months long; the lifetime prevalence (the number of people in the population who have ever manifested the disease) is 4.0 per 1,000; and the lifetime morbid risk (the likelihood that a particular individual will develop schizophrenia in their lifetime) is 7.2 per 1,000. While previous research has shown that men have a higher risk of developing schizophrenia, the researchers found that the prevalence of schizophrenia was the same in men and women (suggesting that the course of the illness differs between the sexes). The prevalence of schizophrenia was lower in poorer countries than in richer countries. What Does This Mean?: Based on these estimates, our textbook numbers on lifetime prevalence and overall risk for an individual to develop schizophrenia are probably too high. Taken together with estimates on the incidence of schizophrenia (that is, the annual number of new cases), it is also clear that current treatments fail to cure most patients with schizophrenia. More Information Online.: Additional information on schizophrenia can be found at the following sources.