Fig. 4.

Phase relationships between habitual sleep-wake and internal circadian time (derived from melatonin sulphate) and external time of day.

The control group had a somewhat late sleep onset but normal circadian entrainment and sleep offset. Schizophrenia subgroup I show an extended sleep period with normal circadian melatonin entrainment. Schizophrenia subgroup II show a marked delay in sleep-wake cycles and melatonin peak relative to time of day, indicating abnormal circadian entrainment in a subset of the schizophrenia group with sleep complaints. Whiskers indicate 95% confidence intervals of the mean.