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Scientists at The Scripps Research Institute Develop Method of Predicting Sleep Patterns Related to Human Performance Errors

April 16, 1996, La Jolla, CA. -- Scientists at The Scripps Research Institute (TSRI) have developed a mathematical method for predicting the time of day at which human biological weaknesses may cause performance errors, often leading to transportation and industrial accidents and injuries.

The work is reported in two articles in the most recent issue of Behavioral Medicine, by Drs. Merrill M. Mitler and James C. Miller of the Laboratory for Sleep, Fatigue and Safety at TSRI.

For decades, scientists have understood the relationship between circadian, or daily, rhythms and human performance and sleepiness. Less well known are the effects of twelve-hour rhythms -- normal, biological functions controlled by the brain -- on performance and sleepiness. The researchers suggest that the daily and twelve-hour rhythms work together to cause sleepiness at night and in the afternoon. The greatest effect at night occurs between midnight and dawn; afternoon sleepiness occurs at siesta time, from approximately 2:00 to 3:00 p.m. According to Mitler, "Evidence exists to suggest that the risk of committing errors during these periods rises sharply compared to the rest of the day and night. Considering only our own biology, humans should be sleeping instead of working during those two portions of the day."

Many statistical analyses, dating back to the 1950s, have shown this two-peak pattern of errors and accidents in the workplace and on the nation's highways. In fact, human mortality follows this pattern as well. People are more likely to die from various diseases in the hours before dawn and in the mid-afternoon than at other times.

The analysis reported by the TSRI scientists demonstrates how the two-peak effect is similar across different kinds of errors, accidents and mortality, and provides a quantitative method of prediction.

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