No evidence for relationship between biorhythms and industrial accidents.

According to the popular biorhythm model accidents are more likely to occur during the "critical days" of three sine wave-like cycles that display periodicities of 23 days, 28 days, and 33 days. Analyses of 400 mining accidents from two separate industries demonstrated that the number of employees who were involved with accidents on their individual critical days of the different cycles did not differ significantly from chance expectancy. Furthermore the number of employees involved in accidents when their cycles were in ascending phases (presumably associated with positive behaviors) did not differ significantly from the number of employees who were involved in accidents when their cycles were in the descending phases, presumably associated with negative behaviors. We have found neither empirical nor theoretical support for the biorhythm model.