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The stability of sleep patterns in children 3 to 7 years of age. OBJECTIVE: To determine the reliability and stability of sleep (duration and quality) over time in young children using repeated accelerometer estimates of sleep. STUDY DESIGN: One hundred ninety-four children wore Actical accelerometers for 5-day periods (24-hour monitoring) at 3, 4, 5, 5.5, 6.5, and 7 years of age. Sleep variables of interest (duration, onset, offset, latency, efficiency, and wake after sleep onset) were estimated using the Sadeh algorithm within a commercial data reduction program (ActiLife). Children were divided into various groups according to sleep stability, and demographic and behavioral differences were compared across groups by ANOVA. RESULTS: All measures of sleep quantity and quality required 4-7 days of accelerometry to obtain acceptable reliability estimates, except morning wake time (2-4 days), and sleep latency (11-21 days). Average year-to-year correlations were only moderate for most measures (r = 0.41-0.51), but considerably higher than those observed for sleep latency, efficiency, and wake after onset (r = 0.15-0.24). Only 29 children were classified as sleep-stable over the 4 years. These children were less likely to be from ethnic minority groups (P = .017) and had higher levels of day-time physical activity (P = .032). CONCLUSIONS: Sleep patterns in children are not particularly stable, showing considerable variation both within a week and across the years. Few children exhibit stable sleep patterns over time, yet characterization of these children might provide further information regarding how sleep benefits health.