Consistency index of daily activity pattern and its correlations with subjective ratings of QOL

Since sleep is under circadian and homeostatic regulation, the status of regulatory mechanisms can be known from daily activity patterns, including both sleep and wake states. Therefore, the relationship between their quantitative characterization and associated subjective QOL can be expected to provide practical knowledge for maintaining/improving QOL. An index quantifying the consistency of daily activity patterns over days, the activity consistency index (ACI), was developed, and its correlations with subjective QOL ratings based on the Pittsburgh sleep quality index (PSQI) and the Kessler Psychological Distress Scale (K6) were analyzed using actigraphy data obtained from university students and IT workers. The consistency of the parametrically transformed actigraphy data was quantified using a parameter set tuned to optimize an ensemble correlation between the consistency measure and QOL. Comparisons of ACI with a previously proposed index (SRI: sleep regularity index) were made according to their correlations with the participants’ subjective ratings of QOL. The comparison of ACI and SRI with respect to the various quantitative features of daily activity revealed that ACI tuned to PSQI was correlated only with mean sleep-onset time and mean sleep duration, while SRI was correlated with most of the quantitative features of sleep. In addition, the correlation profile showed gender dependency. For male and female subjects in their 20 s, the analysis indicated a significant correlation between PSQI and ACI, but not between PSQI and SRI. ACI was shown to work well as an index of daily activity patterns relevant to subjective sleep quality. This ability suggests that ACI could be a basis for predicting subjective sleep quality. Through evaluating daily activity patterns using ACI, an individual may be able to select an appropriate lifestyle for maintaining/improving QOL.