The surprisingly rich contours of schizophrenia epidemiology.

surprised by the data. When new data challenge old beliefs, the field becomes primed for discovery. The aim of this commentary is to let the broader psychiatric community know about recent discoveries in schizophrenia epidemiology , and to speculate on how best to leverage these discoveries to advance knowledge. For those who do not follow the literature closely, recent research in the epidemiology of schizophrenia may come as a surprise. The once cardinal notions that schizophrenia affects men and women equally and is found in all societies with comparable (or equal) incidence are no longer supported by the data. Schizo-phrenia is not the egalitarian disorder that we once thought it was. 1 In this issue of the ARCHIVES, Perälä and colleagues 2 report on what is arguably the most thorough study ever undertaken on the prevalence of psychotic disorders. Overall, the lifetime prevalence of psychotic disorders in Finnish adults was 3.48%. This is a startling proportion. The lifetime prevalence of nonaffective psychoses was 2.29%. For schizophrenia, the lifetime prevalence was 1%, which, while at the higher end of the range, 3 is comparable to other studies from Finland. Regardless of how we partition the psychotic disorders, the survey by Perälä and colleagues 2 reminds us just how common psychotic disorders are in the general population. While they may be less prevalent than depression or substance abuse, we should probably not mislead people by labeling psychoses as low-prevalence disorders. Apart from enumerating cases, what else has epidemiology taught us about schizophrenia? The short message is this: the epidemiology of schizophrenia is no longer a flat and featureless horizon. 4 In its place we find that the epidemiological horizon of schizophrenia 5 is much more interesting than previously suspected. There are rich and informative gradients that can guide future research. For example, a recent systematic review of the incidence of schizophrenia (drawing on 1458 incidence rates from 33 countries) found prominent variation in the incidence of schizophrenia between sites (Ͼ5-fold), and a skewed distribution of rates, with many high rates in the upper tail of the distribution. 6 These data challenge the equal incidence notion promulgated after the publication of the World Health Organization Ten Nation Study. 7 Despite what we read in textbooks and diagnostic manuals, the incidence of schizophrenia is different in men and women. Two systematic reviews have provided convergent evidence that the male-female rate ratio is 1.4:1. 6,8 …