The seasonal incidence of mania and its relationship to climatic variables.

Monthly hospital admission rates (HA) for mania were classified by sex, type of admission (first, or re-admission) and by country (England and Wales or Scotland). Of the 8 classes thus created, all but one showed a statistically significant annual cycle with a peak in Summer and trough in Winter. There was no significant difference in phase or amplitude between male and female cycles. A linear increase in yearly re-admission rates was found during the 8 years of the English and the 11 years of the Scottish data. Current month's mean daily temperature (lag0) and last month's (lag1) mean day-length and mean daily hours of sunshine correlated better with admission rate than did the values for other months. In a multiple regression analysis temperature made the other 2 climatic variables redundant in accounting for variation in HA.