Normative developmental trajectories of actigraphic sleep variables during the preschool period: A three-wave longitudinal study.

Important changes in sleep are believed to occur in the preschool years, but studies that have documented these changes were generally cross-sectional or based on subjective sleep measures. The current longitudinal study modeled the developmental trajectories followed by five sleep variables objectively assessed during the preschool period. Children (N = 128) wore an actigraph over 3 days at 2, 3, and 4 years of age and change in sleep variables was assessed with growth curves. The results showed a linear decrease of daytime, total, and nighttime sleep duration, and a linear increase of sleep efficiency and proportion of nighttime to total sleep. For all sleep variables, the rhythm of change was relatively uniform across children, but there was significant inter-individual variation around the initial status for most variables. To our knowledge, this study is the first to model the developmental trajectories followed by several sleep variables during the preschool period.