Nighttime variability in wrist actigraphy

Wrist actigraphy measures sleep activity and circadian rhythm. This study examined nighttime variability in Actiwatch parameters in a sample of breast cancer survivors (BCSs) to determine a minimum number of nights needed to obtain an accurate picture of objective sleep. A descriptive, quantitative, and repeated measures design was used. Consenting participants wore an actigraph and completed a sleep diary across 7 nights. There were no significant differences in wake after sleep onset (WASO), total sleep time (TST), sleep latency, or sleep disturbances across nights of week (Monday to Sunday) or monitoring nights (1st to 7th). Sleep efficiency was significantly better at Night 6 compared with Night 7. The coefficients of variation (CVs) for WASO ranged from 46% to 86%, TST 23%-34%, sleep latency 154%-246%, sleep efficiency 12%-22%, and sleep disturbances 33%-41%. Although the CVs indicated high variability across women, there was little internight variability in WASO or TST during across 7 nights of sleep. This suggests that in BCSs, Actiwatch data could be collected and evaluated from any single night for an accurate measure of usual sleep.