Global Schizophrenia Prevalence May Have Been Overstated

Schizophrenia may not be as prevalent as generally believed, according to a review of a whopping amount of data from 46 countries.

The study that arrived at this conclusion was conducted by John McGrath, M.D., a professor of psychiatry at the University of Queensland in Australia, and coworkers. Results were published in the May Public Library of Science Medicine.

McGrath and his colleagues systematically reviewed the medical literature on schizophrenia prevalence—that is, the number of people experiencing the illness at a given time or within a time interval—in hopes of coming up with firm figures regarding such prevalence.

This meant that they analyzed 188 studies conducted in 46 countries and published between 1965 and 2002. They also used a sorting algorithm to prevent double-counting of individuals in the same or different studies.

For those studies that reported on lifetime prevalence, the mean lifetime prevalence of schizophrenia (the proportion of individuals in the population who have ever manifested the illness and who are alive on a given day) was 4 per 1,000. DSM-IV-TR states that the lifetime prevalence of schizophrenia is often reported to be 5 to15 per 1,000.

For those studies that reported on point prevalence of schizophrenia (the proportion of individuals who manifest the illness at a given point of time), the mean point prevalence was 4.6 per 1,000. Key policy documents have estimated the point prevalence of schizophrenia to be similar, about 4 per 1,000.

They likewise learned that the lifetime morbid risk of schizophrenia (the probability of a person developing the illness during his or her lifetime) was 7 per 1,000. This estimate corresponds to findings from two other review studies. Moreover, it raises questions about the statement that people often make that “schizophrenia affects about one person in 100,” McGrath and his coworkers pointed out in their report, because the statement is usually based on lifetime morbid risk figures. “If we wish to provide the general public with a measure of the likelihood that individuals will develop schizophrenia during their lifetime, then a more accurate statement would be that `about seven to eight individuals per 1,000 will be affected.'”

The researchers concluded, “While there is substantial variation between sites, generally the prevalence of schizophrenia ranges from 4 to 7 per 1,000 persons, depending on the type of prevalence estimate used.”

The review also suggests, in keeping with some previous studies, that schizophrenia is more prevalent in migrant groups than in native-born populations, adding weight to the argument that migrant status is an important risk factor for the illness.

Yet contrary to some previous findings, the review implies that schizophrenia is about as prevalent among women as among men and that it is not more widespread in urban areas than in rural ones. Both findings surprised McGrath and his colleagues. However, another recent study tends to bolster their gender-related findings: it found a greater prevalence of schizophrenia among females than among males in China.

The study was funded by the Stanley Medical Research Institute.

The report, “A Systematic Review of the Prevalence of Schizophrenia,” is posted online at<http://medicine.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pmed.0020146>.▪