The incidence and temporal patterning of insomnia: a second study

Whether subjects with insomnia exhibit good sleep on some interval basis is unclear. Prior research suggests that patients with insomnia are highly variable with respect to night-to-night sleep continuity, that more than 40% of patients exhibit temporal patterning of good sleep, and that nearly 90% of patients exhibit better than average sleep following 1 to 3 nights of relatively poor sleep. The aim of the present study was to replicate and extend the above-noted findings utilizing: (i) a large sample studied over an extended time interval (ii) absolute standards for 'good' and 'poor' sleep; and (iii) a formal statistical methodology to assess temporal patterning and the association of time in bed with bout duration of poor or average sleep. Thirty-three subjects with insomnia and 33 good sleepers completed sleep diaries over the course of 110 days. It was found that subjects with insomnia (compared to good sleepers) had more poor nights (e.g. about 39 versus 7% of the assessed nights), a higher probability of a having a poor night on any given occasion (60% greater probability than good sleepers) and more consecutive nights of poor sleep between good sleep nights (median bout duration of approximately three versus one night). Lastly, it was found that (as would be predicted by both the Spielman model and the two-process model) time in bed moderated bout duration in the insomnia group. That is, longer times in bed were associated with longer bouts of poor sleep.