Analyzing data gathered in a 10-nation study of psychoses by the World Health Organization (WHO), Susser and Wanderlingfound that the incidence of nonaffective psychoses with acute onset and full recovery was about 10 times higher in premodern cultures than in modern cultures. Transient psychoses with full recovery were comparatively rare in modern cultures.
The WHO studies of psychoses worldwide have made it clear that those with psychoses in general have a better course and outcome in premodern cultures. Some theorists have speculated that the better course and outcome are due to lesser demands made on patients in the agrarian economies of underdeveloped nations. However, further investigations in Japan, Hong Kong, and Singapore—all societies of advanced economic development—have also demonstrated a better course and outcome for psychoses than in Western cultures.