Distributions of hallucinations in the population.

Hallucinations are often manifestations of severe psychiatric conditions seen clinically. However, little is known about the distribution of incident hallucinations in the community, nor whether there has been a change over the past century. Data from the NIMH Epidemiologic Catchment Area Program is used here to provide descriptive information on the community distribution, and data from the Sidgewick study from a century earlier provides comparative information. In the ECA data, the incidence of visual hallucinations was slightly higher in males (about 20 per 1000 per year) than females (about 13 per 1000 per year) across the age span from 18 to 80 years old, with a subsequent increase in the rate for females (up to about 40 per 1000 per year) after age 80. For auditory hallucinations there was an age 25-30 peak in males with a trough for females, and a later age 40-50 peak for females. Overall, there were substantial gender differences, and the effect of aging to increase the incidence of hallucinations was the most consistent and prominent. The Sidgewick study showed a much higher proportion of visual hallucinations than the ECA program. This might be due to factors affecting brain function as well as social and psychological changes over time, although methodological weaknesses in both studies might also be responsible.