Reliability of Actigraphy and Subjective Sleep Measurements in Adults: The Design of Sleep Assessments

Abstract

Study objectives: The aim of the study was to investigate how many nights of measurement are needed for a reliable measure of sleep in a working population including adult women and men.

Methods: In all, 54 individuals participated in the study. Sleep was assessed for 7 consecutive nights using actigraphy as an objective measure, and the Karolinska sleep diary for a subjective measure of quality. Using intra-class correlation and the Spearman-Brown formula, calculations of how many nights of measurements were required for a reliable measure were performed. Differences in reliability according to whether or not weekend measurements were included were investigated. Further, the correlation between objectively (actigraphy) measured sleep and subjectively measured sleep quality was studied over the different days of the week.

Results/conclusions: The results concerning actigraphy sleep measures suggest that data from at least 2 nights are to be recommended when assessing sleep percent and at least 5 nights when assessing sleep efficiency. For actigraphy-measured total sleep time, more than 7 nights are needed. At least 6 nights of measurements are required for a reliable measure of self-reported sleep. Fewer nights (days) are required if measurements include only week nights. Overall, there was a low correlation between the investigated actigraphy sleep parameters and subjective sleep quality, suggesting that the two methods of measurement capture different dimensions of sleep.

Keywords: actigraph; method; repeated measures; sleep diary; sleep efficiency; sleep quality.

Figure 1. Illustration over an actigraphy recording.

Time in bed is the number of minutes between time to bed and get up time. Sleep period is the number of minutes between sleep start and sleep end. The period between time to bed and sleep start is defined as the sleep onset latency.

Figure 2. Presentation of group mean values and 95% confidence intervals over different days of the week, stratified by gender.

Sleep parameters from actigraph presented in graphs 1–3, and subjective sleep quality in graph 4.

Figure 3. Presenting Spearman Brown coefficients (y-axis) by number of days of measurements (x-axis) for All (the full group, n = 49) and when only including participants who had not been working during the weekend (n = 39).

Graph 1–3 present sleep parameters from the actigraphy measures and graph 4 the subjectively reported sleep quality (by index from the sleep diary). Coefficients > 0.7 indicate a satisfactory reliability. The Spearman Brown coefficient for day 1 is equivalent to ICC coefficient for a single measure.