Agreement of objectively measured physical activity and sedentary time in preschool children

AbstractObjectiveTo determine the intra-individual agreement for objectively measured physical activity (PA) and sedentary behavior (SED) over two subsequent weeks in preschool children.MethodNinety-one children aged 3 to 5years (49% boys) from three preschools in Sogn og Fjordane, Norway, provided 14 consecutive days of accelerometer data (Actigraph GT3X+) during the autumn of 2014. Week-by-week reliability was assessed using intraclass correlation (ICC), Bland–Altman plots and 95% limits of agreement for different wear time criteria (≥6, 8 and 10h/day and ≥3 and 5days/week).ResultsThe week-by-week ICC was ≥0.75 for all variables across all wear criteria applied, except for absolute sedentary time (ICC 0.61–0.81). Using a ≥8h/day and ≥3days/week criterion (n=78), limits of agreement were ±209.5cpm for overall PA, ±68.6min/day for SED, ±43.8min/day for light PA, ±20.2min/day for moderate-to-vigorous PA, and ±55.9min/day for light-to-vigorous PA, equaling 1.0–1.6 standard deviation units.ConclusionConsiderable week-by-week variability was found for all variables. Researchers need to be aware of substantial intra-individual variability in accelerometer-measurements and take necessary actions according to the hypothesis under study, as noise in any measurement will preclude researchers' ability to arrive at valid conclusions in epidemiology