Intra-individual variation in children's physical activity patterns: Implications for measurement

Children’s physical activity (PA) patterns change from day to day. This intra-individual variability affects precision when measuring keyphysical activity and sedentary behaviour variables. This paper discusses strategies used to reduce the random error associated with intraindividualvariability and demonstrates the implications for assessing PAwhen varying number of days are sampled. Self-reported data collectedon two hundred and ninety eight 13–14-year-olds were used to compare estimates of PA and sedentary behaviour derived from between 1 and7 days of recall data. Large intra-individual coefficients of variation were calculated for physical activity level (14.5%), moderate-to-vigorousphysical activity (83.4%), screen time (60.8%) and sleep (12.2%). While the magnitude of error associated with estimating means decreasedas more days were sampled, the paper notes that depending on the nature of the research question being asked, sampling fewer days may yieldsufficiently precise estimates. Therefore, researchers should conduct power analyses based on estimated inter- and intra-individual variabilityand sample size to determine how many days to sample when assessing children’s PA patterns.© 2008 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.