The difference between activity when in bed and out of bed. I. Healthy subjects and selected patients.

The activity records of five groups of healthy or ill subjects have been measured for 4-26 days by an accelerometer placed on the nondominant wrist. These data, together with a record of times retiring to/rising from bed, have been used to produce a series of dichotomy indices for comparing the amounts of activity when in bed and out of bed. Reliable differences between individuals were found, with healthy subjects showing a greater degree of dichotomy than one subject with delayed sleep phase syndrome or three subjects with colorectal cancer. The method is convenient for extended data collection and offers the possibility of describing an individual's activity profile in a variety of circumstances.