0191 Evaluating Sleep Intra-Individual Variability: Relationships with Sleep Quality, Sleepiness, and Time Management

Abstract Introduction Intra-individual variability (IIV) in sleep is increasingly studied for its association with health, beyond mean sleep characteristics. However, measuring sleep IIV can be challenging without actiwatches or multi-day sleep diaries. To enable efficient one-time assessment of IIV in various sleep domains, we developed and updated the Sleep Intra-individual Variability Scale version 2 (SIIV). We evaluated the internal consistency of the SIIV and investigated the relationship between sleep IIV, sleep quality, sleepiness, and time management. Methods We asked 374 first-year college students (mean age=18.34, SD=0.85; 73.26% female) to complete the SIIV, the Pittsburgh Sleep Quality Index, Epworth Sleepiness Scale, and the Time Management Questionnaire. The SIIV asked for typical sleep characteristics on every day of the week, in five domains: bedtime, risetime, total sleep time (TST), sleep onset latency (SOL), and napping. Individual standard deviations of sleep characteristics were calculated to represent IIV in sleep domains. Cronbach’s alpha, t-tests, and Pearsons’ correlations were conducted. Results IIVs in the five sleep domains were relatively independent (Cronbach’s alpha=0.39). We found a strong correlation between IIVs in TSTs and IIVs in risetimes (r=0.60, p 0.001), but all other domains were weakly-to-moderately correlated (rs.30). Non-white students reported greater IIV in TST than white students (non-white: 1.00±0.60h; white: 0.83±0.54h; p=0.005) and risetime (non-White: 74.86±40.88min; White: 65.82±36.19min; p=0.027). Females reported greater IIV in SOL than males (females: 4.92±5.07min; male: 3.35±3.91min; p=0.002). After controlling for mean sleep characteristics, poorer sleep quality was associated with greater IIV in TST (r=0.30, p 0.001), risetime (r=0.19, p 0.001), and SOL (r=0.16, p=0.002). Greater IIV in TST (r=0.16, p=0.002) and SOL (r=0.21, p 0.001) also correlated with greater daytime sleepiness, after adjusting for mean TST and SOL, respectively. In addition, greater IIV in TST (r=-0.12, p=0.021) was associated with poorer time management, after adjusting for mean TST. Conclusion Greater IIV in sleep, especially TST, was associated with demographics, poor sleep quality, sleepiness, and poor time management. A single timepoint, self-reported measure of IIV increases the feasibility of estimating nightly consistency/regularity across five sleep domains. Support (if any) National Science Foundation (1920730 and 1943323)