• Biorhythm, a theory that purports to identify periods of increased individual susceptibility to accident or misfortune on the basis of recurring biological cycles, is currently enjoying world-wide popularity. In view of the implications of such a theory for both public health and safety, the present study was undertaken as an empirical test of its validity. Using data from 205 carefully investigated highway crashes (135 fatal; 70 nonfatal) in which the drivers were clearly at fault, the authors computed specific points in drivers' biorhythm cycles at which the accidents occurred. The observed frequencies of accidents occurring during so-called critical and minus periods were then compared with the frequencies to be expected on a chance basis alone. The results provided no evidence for a relationship between purported biorhythm cycles and accident likelihood.
Shaffer JW, Schmidt CW, Zlotowitz HI, Fisher RS. Biorhythms and Highway CrashesAre They Related?. Arch Gen Psychiatry. 1978;35(1):41-46. doi:10.1001/archpsyc.1978.01770250043003