Schizophrenia is a devastating mental illness and a major contributor to the global burden of disease, but how many people are actually suffering from the disease worldwide? John McGrath and colleagues from the University of Queensland have conducted the most comprehensive analysis on the topic and now report their findings in the May issue of the international open-access journal PLoS Medicine. The researchers have done what is called a systematic review of the medical literature, which turned out a few surprises. And knowing about prevalence--defined as the number of people suffering from the disease at a given time or within a time interval--of such an important disease is crucial to health policy strategies. They found that schizophrenia is more common in developed than in poorer countries but overall less common than previously thought. Across countries, immigrants have higher rates of the disease than native-born individuals.

The scientists have analyzed a total of 1,721 estimates from 188 studies covering 46 countries and calculated the following median prevalence estimates: 4.6 per 1,000 for point prevalence (defined as prevalence during any interval of less than a month), 3.3 for period prevalence (defined as prevalence during a period from 1 to 12 months), 4.0 for lifetime prevalence (the proportion of individuals in the population who have ever manifested the disease and who are alive on a given day), and 7.2 for lifetime morbid risk (which attempts to include the entire lifetime of a birth cohort, both past and future, and includes those deceased at the time of the survey).

The point prevalence numbers are consistent with key policy documents, but the 0.5% estimate for lifetime prevalence given in many textbooks is a significant overestimate. "This," the authors suggest, "is another example where the research community needs to review their belief systems in the face of data." Another often quoted statistic, namely that "schi
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Contact: Paul Ocampo
pocampo@plos.org
415-624-1224
Public Library of Science
30-May-2005

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