Weekly variation in sleep patterns: Estimates of validity in Japanese schoolchildren

Because sleep indices vary during school-days and weekends, we examined the validity of self-reported estimates of sleep patterns in junior high schoolchildren through a comparison of questionnaire, actigraphy, and diary-reported sleep patterns during 1 week. Questionnaires and daily logs were compared with objective sleep parameters derived from Actiwatch, a sleep monitoring actigraph, in a sample of 91 13-14-year-old children (47 girls, 44 boys). Pearson's and Spearman's correlation coefficients, and paired t-tests were used to evaluate the correlation and difference between subjective and objective sleep parameters. School-night sleep start and the sleep period estimated by the diary did not differ from the amount recorded by actigraphy, although sleep latency in the diary was longer. A significant difference between subjective-diary and objective actigraphy correlation (after z-transformation) was found between school-days and weekends for sleep latency in boys, the sleep period in girls and total sleep period. Strengths of the associations were consistently higher at the beginning of the experiment, gradually decreasing. Objectively, the number of night awakenings was almost twofold higher among boys in comparison to girls. When compared with actigraphy, daily log correlations showed higher values than the questionnaire. Our results support the validity of the subjective estimates in comparison with actigraphy. Children cannot estimate some subjective sleep parameters exactly, especially those relating to night awakening and sleep efficiency, although the correlation coefficients showed relatively high values. School-day reports tend to be more reliable than weekend reports. School-days, weekends, and gender should be controlled in surveys as confounding variables.