The utility and validity of daytime naps in the assessment of sleep-onset insomnia.

This study examined the discriminant validity, consistency, and reactivity of afternoon naps for assessing sleep-onset insomnia. Eleven insomniac and 17 noninsomniac subjects came to a sleep laboratory for three afternoon naps while multiple electrophysiological and subjective measures were taken. The results indicated that sleep-onset latencies during the afternoon naps significantly discriminated between insomniac and noninsomniac subjects. Further, significant correlations were found among most measures of sleep-onset latency measured both electrophysiologically and subjectively. The proportion of variance in sleep-onset latency accounted for by groups (insomniac vs. noninsomniac) increased over the three naps. Finally, a comparison of the results from this study with those from three all-night studies using identical facilities and procedures revealed that the sleep-onset latencies from this nap study were within the ranges expected on the basis of the all-night studies.