A novel index for actigraphic studies: The core sleep efficiency.

Sleep efficiency is a widely used indicator of sleep quality in actigraphy studies. Nevertheless, it is a composite metric integrating data derived from actigraphic recordings alongside information about bedtime and wake-up time, typically obtained from self-reported sleep logs. The aim of this report is to propose a novel sleep efficiency index, denoted as core sleep efficiency, that relies solely on actigraphic data and focuses on the quality of sleep after its onset. Using a database of actigraphic recordings obtained in 40 young subjects (22 ± 3 yrs, Mean±SD) and in 45 middle-aged subjects (63 ± 11 yrs, Mean±SD), we evaluated the interrelationship between the two metrics of sleep efficiency and investigated the extent of their correlation with other crucial actigraphic indicators of sleep quality, such as sleep onset latency, fragmentation index and mean activity score. We provided evidence suggesting that the novel index may be suitable for specifically assessing the quality of sleep once it has begun. We propose that the newly introduced core sleep efficiency has the potential to serve as a valuable adjunct to the classic sleep efficiency, thus enriching the parametric characterisation of sleep obtained through actigraphy.