Psychometric properties of two systematic observation techniques for assessing physical activity levels in children with mental retardation

This study examined the psychometric properties of the System for Observing Fitness Instruction Time (SOFIT) and the Children's Activity Rating Scale (CARS) for use with children with mental retardation (MR). Eleven children with MR were videotaped while participating in a university-based community outreach program. Actimatch accelerometers were used as the criterion measure. Results indicated that SOFIT and CARS both demonstrated adequate levels of generalizability (phi= 0.98 and 0.75), but a low concurrent validity coefficient for SOFIT (r =. 10) and a moderate level of validity coefficient for CARS (r = .61) were observed. CARS demonstrates stronger validity evidence than SOFIT, but it is important to have sufficient rater training before using CARS for measuring physical activity level of children with MR.