Assessing Volume of Accelerometry Data for Reliability in Preschool Children

1Interdisciplinary Educational Research Institute, University of Wollongong, Wollongong, New South Wales, Australia 2Centre for Physical Activity and Nutrition Research, Deakin University, Burwood, Victoria, Australia.
Medicine and science in sports and exercise (Impact Factor: 3.98). 07/2012; 44(12). DOI: 10.1249/MSS.0b013e3182661478
Source: PubMed

This study examines what volume of accelerometry data (h·d) is required to reliably estimate preschool children's physical activity and whether it is necessary to include weekday and weekend data.

Accelerometry data from 493 to 799 (depending on wear time) preschool children from the Melbourne-based Healthy Active Preschool Years study were used. The percentage of wear time each child spent in total (light-vigorous) physical activity was the main outcome. Hourly increments of daily data were analyzed. t-tests, controlling for age and clustering by center of recruitment, assessed the differences between weekday and weekend physical activity. Intraclass correlation coefficients estimated reliability for an individual day. Spearman-Brown prophecy formula estimated the number of days required to reach reliability estimates of 0.7, 0.8, and 0.9.

The children spent a significantly greater percentage of time being physically active on weekend compared with weekdays regardless of the minimum number of hours included (t = 12.49-16.76, P < 0.001 for all). The number of days required to reach each of the predetermined reliability estimates increased as the number of hours of data per day decreased. For instance, 2.7-2.8 d of data were required to reach a reliability estimate of 0.7 with 10 or more hours of data per day; 3.3-3.4 d were required to meet the same reliability estimate for days with 7 h of data.

Future studies should ensure they include the minimum amount of data (hours per day and number of days) as identified in this study to meet at least a 0.7 reliability level and should report the level of reliability for their study. In addition to weekdays, at least one weekend day should be included in analyses to reliably estimate physical activity levels for preschool children.

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    • "Especially triaxial accelerometers are valid devices with similar classification accuracy for sedentary, light, and moderate-to-vigorous levels of PA in preschoolers [19]. However, in order to obtain reliable data, a minimum amount of measured days/daily hours of measurement should be obtained, and at least one weekend day should be included in analyses to reliably estimate physical activity levels for preschool children [20]. In our study, PA was measured by accelerometers (SenseWear Pro 2, Bodymedia, SMT medical GmbH&Co Würzburg, Germany [21], [22] over a period of 7 consecutive days, thereby including one weekend. "
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    ABSTRACT: Data on objectively measured physical activity (PA) in preschoolers are controversial. Direct accelerometry was performed in children aged 3-6 years, and differences in PA patterns over the course of the week were evaluated. Data were analyzed with gender, BMI, lifestyle, and socioeconomic parameters as covariates. PA was measured in 119 children by the SensewearPro® accelerometer and analyzed in the 92 (40 girls) that wore it for at least 4 days including one day of the weekend. Median measuring time in this group was 7 consecutive days (median/mean daily measuring time: 23.5 h/d and 21.8 h/d, respectively), corresponding to 834,000 analyzed minutes. PA questionnaires were completed by 103 parents and 87 preschool teachers to collect anthropometric, lifestyle, and socioeconomic data. Median daily PA (MET>3) was 4.3 hours (mean: 4.4 hours). Boys spent an estimated 52 min/week more being very active (MET>6) than girls (95% CI [6, 96] min/week, p = 0.02). PA was lower during the weekend (3.7 h/d) compared to weekdays (4.5 h/d), p = 3×10(-6)), where a 95% CI for the difference is [0.5, 1.0] h/d. PA levels did not differ between overweight/obese children (median 4.7 h/d) and normal-weight peers (median 4.2 h/d). Daily media consumption increased with decreasing social class on weekdays (p = 0.05) and during the weekend (p = 0.01), but was not related to the amount of daily PA. A multivariate regression with BMI-SDS as independent variable and gender, age, amount of PA>6 MET, parental BMI, media time and socioeconomic status as explanatory variables revealed that only SES had a significant contribution. The negative impact of obesity-promoting factors in older children is rather low for preschoolers, but there is evidently a gradient in PA between weekdays and weekends already in this age group. Weight status of preschoolers is already considerably influenced by SES, but not physical activity levels.
    PLoS ONE 04/2013; 8(4):e60619. DOI:10.1371/journal.pone.0060619 · 3.23 Impact Factor
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    ABSTRACT: When using accelerometers to measure physical activity, researchers need to determine whether subjects have worn their device for a sufficient period to be included in analyses. We propose a minimum wear criterion using population-based accelerometer data, and explore the influence of gender and the purposeful inclusion of children with weekend data on reliability. Accelerometer data obtained during the age seven sweep of the UK Millennium Cohort Study were analysed. Children were asked to wear an ActiGraph GT1M accelerometer for seven days. Reliability coefficients(r) of mean daily counts/minute were calculated using the Spearman-Brown formula based on the intraclass correlation coefficient. An r of 1.0 indicates that all the variation is between- rather than within-children and that measurement is 100% reliable. An r of 0.8 is often regarded as acceptable reliability. Analyses were repeated on data from children who met different minimum daily wear times (one to 10 hours) and wear days (one to seven days). Analyses were conducted for all children, separately for boys and girls, and separately for children with and without weekend data. At least one hour of wear time data was obtained from 7,704 singletons. Reliability increased as the minimum number of days and the daily wear time increased. A high reliability (r = 0.86) and sample size (n = 6,528) was achieved when children with ≥ two days lasting ≥10 hours/day were included in analyses. Reliability coefficients were similar for both genders. Purposeful sampling of children with weekend data resulted in comparable reliabilities to those calculated independent of weekend wear. Quality control procedures should be undertaken before analysing accelerometer data in large-scale studies. Using data from children with ≥ two days lasting ≥10 hours/day should provide reliable estimates of physical activity. It's unnecessary to include only children with accelerometer data collected during weekends in analyses.
    PLoS ONE 06/2013; 8(6):e67206. DOI:10.1371/journal.pone.0067206 · 3.23 Impact Factor
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