Rich, C; (2013) Methodological considerations in large scale accelerometer-based studies of childhood physical activity. Doctoral thesis , UCL (University College London).

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Abstract

Accelerometers are widely used to measure children’s physical activity (PA) in large scale studies. However, the analysis of data from such studies is challenging and several methodological uncertainties remain regarding collection and processing protocols. The aim of this thesis was to investigate some of these issues in relation to a range of child and parental factors using data collected as part of the Millennium Cohort Study (MCS). The MCS is a UK-wide prospective study of the social, economic and health-related circumstances of children. Accelerometer-determined measurement of activity was introduced into the study when the children were aged seven years. Accelerometers were distributed and returned using a novel postal methodology. Reliable accelerometer data was obtained from 7,105 children. Analyses were conducted to determine: (i) data processing thresholds; (ii) predictors of consent, accelerometer return, and data acquisition, and; (iii) factors associated with intra-individual variation of PA and sedentary behavior (SB) across the four seasons. Analyses revealed that: (i) using a proposed minimum threshold of 11,715 counts/minute will enable researchers to identify extreme high count values in the ActiGraph GT1M, and using data from children with ≥ two days lasting ≥ six hours/day will provide reliable estimates of children’s habitual PA; (ii) a range of factors are associated with non-response, and; (iii) a single-measurement period may not adequately measure children’s activity due to substantial intra-individual variation in PA and SB across the seasons. Some children are also less stable in their activity and may therefore be more amenable to change. Interventions aimed at reducing SB and/or increasing PA may be particularly helpful for these groups of children. 4 These findings highlight the importance of quality control procedures in accelerometer data collection and processing. This thesis addresses methodological issues in large scale accelerometer-based studies of childhood activity and presents important results in this area.

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