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
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
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
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
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.