Which are the Central Aspects of Infant Sleep? The Dynamics of Sleep Composites across Infancy.

Sleep during infancy is important for the well-being of both infant and parent. Therefore, there is large interest in characterizing infant sleep with reliable tools, for example by combining actigraphy with 24-h-diaries. However, it is critical to select the right variables to characterize sleep. In a longitudinal investigation, we collected sleep data of 152 infants at ages 3, 6, and 12 months. Using principal component analysis, we identified five underlying sleep composites from 48 commonly-used sleep variables: , , , , . These composites accurately reflect known sleep dynamics throughout infancy as (representing naps), (representing sleep efficiency and consolidation), and (representing day-to-day stability) decrease across infancy, while (representing nighttime sleep) slightly increases, and becomes earlier as one ages. We uncover interesting dynamics between the sleep composites and demonstrate that infant sleep is not only highly variable between infants but also dynamic within infants across time. Interestingly, is associated with behavioral development and therefore a potential marker for maturation. We recommend either the use of sleep composites or the core representative variables within each sleep composite for more reliable research.