Measuring sleep: accuracy, sensitivity, and specificity of wrist actigraphy compared to polysomnography

Abstract

Objectives: We validated actigraphy for detecting sleep and wakefulness versus polysomnography (PSG).

Design: Actigraphy and polysomnography were simultaneously collected during sleep laboratory admissions. All studies involved 8.5 h time in bed, except for sleep restriction studies. Epochs (30-sec; n = 232,849) were characterized for sensitivity (actigraphy = sleep when PSG = sleep), specificity (actigraphy = wake when PSG = wake), and accuracy (total proportion correct); the amount of wakefulness after sleep onset (WASO) was also assessed. A generalized estimating equation (GEE) model included age, gender, insomnia diagnosis, and daytime/nighttime sleep timing factors.

Setting: Controlled sleep laboratory conditions.

Participants: Young and older adults, healthy or chronic primary insomniac (PI) patients, and daytime sleep of 23 night-workers (n = 77, age 35.0 ± 12.5, 30F, mean nights = 3.2).

Interventions: N/A.

Measurements and results: Overall, sensitivity (0.965) and accuracy (0.863) were high, whereas specificity (0.329) was low; each was only slightly modified by gender, insomnia, day/night sleep timing (magnitude of change < 0.04). Increasing age slightly reduced specificity. Mean WASO/night was 49.1 min by PSG compared to 36.8 min/night by actigraphy (β = 0.81; CI = 0.42, 1.21), unbiased when WASO < 30 min/night, and overestimated when WASO > 30 min/night.

Conclusions: This validation quantifies strengths and weaknesses of actigraphy as a tool measuring sleep in clinical and population studies. Overall, the participant-specific accuracy is relatively high, and for most participants, above 80%. We validate this finding across multiple nights and a variety of adults across much of the young to midlife years, in both men and women, in those with and without insomnia, and in 77 participants. We conclude that actigraphy is overall a useful and valid means for estimating total sleep time and wakefulness after sleep onset in field and workplace studies, with some limitations in specificity.

Keywords: Actigraphy; WASO; accuracy; polysomnography; sensitivity; specificity.

Figure 1

Kernel Density Estimates of the distribution of individual accuracy, sensitivity and specificity in the study. Sensitivity reflects the proportion of 30-sec epochs actigraphically defined correctly as sleep relative to the gold standard PSG. Specificity reflects the proportion of epochs correctly assigned as wake. Accuracy refers to the proportion of correctly characterized epochs relative to all epochs.

Figure 2

Age effect on accuracy, sensitivity, and specificity of actigraphy on PSG based on GEE multivariate regression adjusting for gender, time of sleep, and chronic primary insomnia.

Figure 3

(A) PSG WASO vs. actigraphy WASO scatterplot and their corresponding histograms. The dashed black line is the 45-degree line. The solid gray line is the line of best fit and the gray dashed lines are the confidence band of the line of best fit. (B) Bland-Altman plot of individual differences between actigraphy and PSG for WASO. The solid black horizontal line at zero denotes the scenario when no bias is present. The dashed gray line represents the best line of agreement based on the linear spline regression model describing mean change in bias over average WASO and the solid gray lines are the 95% limits of agreement. The dotted black line represents the overall mean bias.