Refining sleep measurement using the Motionwatch8©: how many days of monitoring do we need to get reliable estimates of sleep quality for older adults with mild cognitive impairment?

Poor sleep is common among older adults with mild cognitive impairment (MCI)—a transition stage between healthy cognition and dementia. Objective, reliable, and low-burden field methods to measure older adult sleep are also currently needed. The MotionWatch8© (MW8) wrist-worn actigraph provides estimates of sleep with 14 days of observation; however, there may be underlying differences in the reliability of sleep estimates based on MCI status. We therefore investigated the number of MW8 monitoring days required to estimate sleep in older adults with MCI and without. Older adults (55+ years; N = 151) wore the MW8 for ≥14 days. The Montreal Cognitive Assessment was used to categorize participants with probable MCI (scores of < 26/30) and participants without MCI (≥ 26/30). We calculated intra-class reliability coefficients for one, seven, and 14 days of wear-time, and performed Spearman-Brown predictions to determine the number of monitoring days needed for an ICC = 0.80. Older adults with MCI were older (p < 0.01), more likely to be male (p = 0.03), and had shorter sleep duration (p < 0.01). Spearman-Brown analyses indicated that the number of monitoring days needed for an ICC = 0.80 in older adults with probable MCI was 7 days for sleep duration, 4 days for fragmentation, and 4 days for efficiency; adults without MCI required 4 days for duration, 6 days for fragmentation, and 3 days for efficiency. Our results indicate that while the reliability of MW8 estimates of sleep differs based on cognitive status, 7 days of MW8 monitoring provides reliable estimates of sleep for adults with MCI and those without.