Circadian variation in suicide attempts in Tokyo from 1978 to 1985

Circadian variations in suicide attempts in Tokyo from 1978 to 1985 were analyzed on the basis of records of the Ambulance Service of Tokyo. A significant circadian variation in suicide attempts was demonstrated by the cosinor method, power spectrum analysis (by the maximum-entropy method), and analysis of variance. The peak time for suicide attempts was established by cosinor analysis as about 1800 hours (6:00 P.M.). The circadian variation in suicide attempts seemed to be associated with endogenous rhythms such as mood, as well as with daily variation in social activities.