title: The minimum number of days required to establish reliable physical activity estimates in children aged 2-15 years.
abstract: The purpose of this study was to determine the minimum number of days needed to assess reliable estimates of step-count data for children based on age and gender. A total of 428 developing children (at least 30 boys and 30 girls in seven two-year intervals from 2-3 years to 14-15 years of age) wore a StepWatch accelerometer for 7 consecutive days. Following data screening, the 422 children's data were finally analyzed by age and sex groups using the Generalizability theory. Single-facet crossed designs (i.e. Participant (P) × Days (D)) were applied for each of 14 datasets. G-studies were performed to quantify the percentage of variance associated with the facet and interaction in the model. Follow-up D-studies were performed to determine the minimum number of days of step-count data collection needed to achieve a desirable reliability coefficient (G ≥ 0.80). The results from the G-studies show that P explained a large percentage of the total variance (26-71%) while D had little effect on the total variance (0-5%). A relatively large percentage of variance was unidentified (i.e. the P × D interaction). The minimum number of days necessary to achieve a desirable reliability coefficient (G ≥ 0.80) ranged from 2 to 12 d. On average, boys required less days of monitoring than girls. Researchers should use the findings of this study to design data collection that ensures reliable data.
authors.affiliation: Department of Health and Human Performance, Middle Tennessee State University, Murfreesboro, TN, USA.
authors.forename: Minsoo
authors.initials: M
authors.lastname: Kang
authors.forename: Kristie
authors.initials: K
authors.lastname: Bjornson
authors.forename: Tiago V
authors.initials: TV
authors.lastname: Barreira
authors.forename: Brian G
authors.initials: BG
authors.lastname: Ragan
authors.forename: Kit
authors.initials: K
authors.lastname: Song
mesh_terms: D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D008297:Male; D018670:Monitoring, Ambulatory / Q000379:methods*; D009043:Motor Activity; D015203:Reproducibility of Results; D013997:Time Factors