Estimated Distributions of Usual Physical Activity during Recess.

Purpose: This study aimed to estimate distributions of usual physical activity during recess in schools in low-income areas using measurement error models and to compare model-adjusted distributions to unadjusted distributions based on a single day of measurement.

Methods: A randomized study of the Playworks program was conducted in 29 schools from six U.S. cities. A sample of 365 fourth- and fifth-grade students in 26 of the study schools wore accelerometers during their recess periods on two school days. Estimates for the percentage of time spent in moderate to vigorous physical activity (MVPA) during recess were constructed from the accelerometer data for each school day. Using measurement error models, distributions for the usual amount of time spent in MVPA during recess were estimated for intervention and control groups of males and females. Unadjusted distributions for these same groups were also constructed using data from a single school day.

Results: There is considerable intraindividual variability in the students' physical activity, which accounts for 67%-83% of the overall variability, depending on the study group. Unadjusted single-day distributions are much wider and have more weight in the tails than model-adjusted distributions owing to this large intraindividual variability in the data.

Conclusions: Using measurement error models to analyze physical activity data collected from recess periods will allow for more accurate and reliable inferences on students' physical activity.