Figure 1.

Raster plots of the timing of work (white bars), sleep (grey bars), in-shift alertness testing (closed circles) and aMT6s acrophase (diamonds) for two intensive care doctors (a,b) and nurses (c,d). Error bars on the diamonds represent 95% confidence intervals of the timing of acrophase. Doctors worked 7 day shifts, followed by 7 day offs and 7 consecutive night shifts. Nurses worked irregular rotations between day, evening and night shifts. Night shifts were sometimes associated with frequent napping during the shifts (a) and often a small delay in circadian timing (a,c). Sleep during the day was usually considerably shorter than night sleep (b,c). Sleep duration between evening and day shift was considerably truncated (c,d). Alertness and performance data from doctors tested on the 7^th night shift are not reported in this manuscript.