Document Type

Open Access Thesis

Embargo Period


Degree Program


Degree Type

Master of Science (M.S.)

Year Degree Awarded


Month Degree Awarded



INTRODUCTION: Direct observation (DO) systems have been used for decades to assess free-living PA in children. These traditional DO systems identify the highest intensity observed during alternating observe-and-record periods. Using video-taped DO would allow researchers to code activities and contextual information each time the participant changes their behavior. PURPOSE: To develop and test a novel video-based DO system for children’s free-play activity. METHODS: Following iterative DO system development (The Observer XT, Noldus), 28 children (age=8.4 ± 1.5 years) participated in a 30-minute simulated free-play session that was recorded with a GoPro camera. Participants wore a portable indirect calorimetry (IC) device and an accelerometer on the hip (AG-H) and non-dominant wrist (AG-W). The DO system includes Whole Body Movement (body position, main movement pattern) that was further described with four modifiers: 1) Locomotion, 2) Limb Movement, 3) Activity Type, and 4) MET value. To assess intrarater reliability, an expert coder coded six randomly selected videos from the main sample and recoded the same videos one week later. Six novice coders were trained and coded three videos from the subsample to assess interrater reliability. To assess construct validity, total energy expenditure and time spent in activity intensity categories from DO were compared with IC and accelerometer estimates. RESULTS: Percent agreement for intrarater reliability was above 80% except for Locomotion (47%; video 3) and Limb Movement, MET value and Locomotion (19%, 78%, 26%), respectively, video 4). Across all variables, percent agreement for interrater reliability ranged widely from 12%-96%, 0-100%, and 36%-97% for videos 1, 2 and 3, respectively. Mean estimated time spent in PA intensity categories from AG-H overestimated sedentary (SED) and underestimated light, moderate, and moderate-to-vigorous PA (LPA, MPA, and MVPA; p < 0.001-0.008). AG-W and IC underestimated SED (p=0.03, p=0.03) and LPA (p< 0.001, pONCLUSION: The current DO system is feasible for observing detailed changes in children’s free-play activity. However, refinement to the system must be made to improve reliability before it is adopted as a criterion measure for free-play activity in children.

First Advisor

John Sirard, PhD