Subjective sleep measurement: comparing sleep diary to questionnaire

The sleep diary is the gold standard of self-reported sleep duration, but its comparability to sleep questionnaires is uncertain. The purpose of this study was to compare self-reported sleep duration between a sleep diary and a sleep questionnaire and to test whether sleep-related disorders were associated with diary-questionnaire differences in sleep duration.

We compared self-reported sleep duration from 5,432 questionnaire-sleep diary pairs in a longitudinal cohort of 1,516 adults. Participants reported sleep information in seven-day sleep diaries and in questionnaires. Research staff abstracted average sleep durations for three time periods (overall; weekday; weekend) from diaries and questionnaires. For each time period, we evaluated diary-questionnaire differences in sleep duration with Welch's two-sample t-tests. Using linear mixed effects regression, we regressed overall diary-questionnaire sleep duration difference on several participant characteristics: reporting any insomnia symptoms, having sleep apnea, sex, body mass index, smoking status, Short Form-12 Physical Health Composite Score, and Short Form-12 Mental Health Composite Score.

The average diary-reported overall sleep duration (7.76 hrs) was longer than that of the questionnaire (7.07 hrs) by approximately 41 mins (0.69 hrs, 95% confidence interval: 0.62, 0.76 hrs). Results were consistent across weekday- and weekend-specific differences. Demographic-adjusted linear mixed effects models tested whether insomnia symptoms or sleep apnea were associated with diary-questionnaire differences in sleep duration. Insomnia symptoms were associated with a 17 min longer duration on the diary relative to the questionnaire (β=0.28 hrs, 95% confidence interval: 0.22, 0.33 hrs), but sleep apnea was not significantly associated with diary-questionnaire difference. Female sex was associated with greater diary-questionnaire duration differences, whereas better self-reported health was associated with lesser differences.

Diaries and questionnaires are somewhat disparate methods of assessing subjective sleep duration, although diaries report longer duration relative to questionnaires, and insomnia symptoms may contribute to greater perceived differences.