How many nights are enough? The short-term stability of sleep parameters in elderly insomniacs and normal sleepers

Temporal stability is an important fundamental quality when measuring sleep parameters, yet it has been infrequently assessed. Generalizability theory was used to estimate the short-term temporal stability of five variables c ommonly used to characterize insomnia: sleep onset latency, total sleep tim e, wake after sleep onset, time in bed, and sleep efficiency. Estimates wer e calculated for 32 elderly primary insomniacs and 32 elderly normal sleepe rs, both in the lab and at home, using both sleep logs and polysomnography (PSG). A week of recording using either PSG or sleep logs was typically suf ficient to achieve adequate stability (defined as G coefficient of at least 0.80) with some notable exceptions: (a) when using log-derived measures wi th insomniacs, a 3-week average was necessary for wake after sleep onset an d (b) more than a 2-week average was necessary for sleep onset latency. Bec ause of the substantial commitment involved in the physiological recording of sleep, alternative forms of aggregation are considered with the intent o f improving temporal stability.