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  • Original Article
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Impact of methodological decisions on accelerometer outcome variables in young children



The impact of accelerometer-related methodological decisions relating to the assessment of physical activity and sedentary time has not been conclusively determined in young children.


To determine the effects of epoch and cutoff points on the assessment of physical activity and sedentary time and to determine the accelerometer wear time required to achieve reliable accelerometer data in children.


Children were recruited from centres at Ghent, Glasgow, Gothenburg and Zaragoza.


Physical activity was assessed for 1 week in 86 children (41 girls, 45 boys; mean age 7±2 years) by uniaxial accelerometry. The epoch was set at 15 s and reintegrated to 30 and 60 s. Time spent sedentary and in moderate and vigorous physical activity (MVPA) was assessed using a range of cutoff points. Number of days required to achieve 80% reliability was predicted using the Spearman–Brown Prophecy formula.


The Reilly cutoff points (<1100 counts per min (CPM)) indicated less sedentary time per day when comparing 15 vs 30 s and 15 vs 60 s epochs: 570±91 vs 579±93 min and 570±91 vs 579±94 min, respectively; P<0.05. Pate cutoff points (>420 counts per 15 s) reported more MVPA time per day compared with Sirard (890 counts per 15 s) and Puyau cutoff points (>3200 counts per min) using 15 s epoch: 78 (4–197) min (median (range) vs 18 (1–80) min and 24 (1–100) min, respectively; P<0.001. Compliance with guidelines of at least 60 min MVPA was 84, 78 and 73% for Pate cutoff points using 15, 30 and 60 s epochs, respectively, but 0% for Sirard and Puyau cutoff points across epochs. The number of days required to achieve 80% reliability for CPM, sedentary and MVPA time was 7.4–8.5 days.


Choice of epoch and cutoff point significantly influenced the classification of sedentary and MVPA time and observed compliance to the MVPA guidelines.

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We thank all members of the validation study and especially the children and their parents for their enthusiastic participation in the study. This study was conducted as part of the IDEFICS study and is published on behalf of its European Consortium ( We gratefully acknowledge the financial support of the European Community within the Sixth RTD Framework Programme Contract No. 016181 (FOOD).

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Correspondence to Y P Pitsiladis.

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Statement of ethics

We certify that all applicable institutional and governmental regulations pertaining to the ethical use of human volunteers were followed during this research. Approval by the appropriate ethics committees was obtained by each of the eight centres engaged in the fieldwork. Participants were not subjected to any procedure before both the children and their parents gave consent for examinations, collection of samples, subsequent analysis and storage of personal data and collected samples. The participating children and their parents could consent to single components of the study while refraining from others.

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Ojiambo, R., Cuthill, R., Budd, H. et al. Impact of methodological decisions on accelerometer outcome variables in young children. Int J Obes 35 (Suppl 1), S98–S103 (2011).

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