Different analysis methods of Scottish and English child physical activity data explain the majority of the difference between the national prevalence estimates

BackgroundThe percentage of children in Scotland and England meeting the aerobic physical activity recommendation differ greatly according to the estimates derived from the respective national health surveys. The Scottish Health Survey (SHeS) usually estimates that over 70% meet the guidelines; Health Survey for England (HSE) estimates are usually below 25%. It is plausible that these differences originate from different analysis methods. The HSE monitor the percentage of children that undertake 60 minutes of moderate-to-vigorous physical activity on each day of the week (‘the daily minimum method’ (DMM)). The SHeS monitor the proportion that undertake at least seven sessions of moderate-to-vigorous physical activity, with an average daily duration over 60 minutes (‘the average method’ (WAM)). We aimed to establish how great an influence this difference in analysis methods has on the prevalence estimates.MethodsPhysical activity data from 5-15 year olds in the 2015 HSE and SHeS were reanalysed (weighted n=3840 and 965, respectively). Two comparable pairs of estimates were derived: a DMM and WAM estimate from the HSE not including travel to/from school, and WAM estimates from the HSE and the SHeS including travel to/from school. It is not possible to calculate a DMM estimate from the SHeS due to the way the questions are asked. Results were presented for the total samples, and by sex and age sub-groups.ResultsThe HSE WAM estimate was 31.7 (95% CI: 30.2-33.3) percentage points higher than the DMM estimate (54.3% (95% CI: 52.6-56.0) and 22.6% (95% CI: 21.2-24.1) respectively). The magnitude of this difference differed by age group but not sex. When comparable WAM estimates were derived from the SHeS and the HSE, the SHeS was 11.8 percentage points higher (73.6% (95% CI: 69.8-77.1) and 61.8% (95% CI: 60.2-63.5) respectively). The magnitude of this difference differed by age group and sex.ConclusionsThe results indicate that the difference in the analysis method explains the majority (approximately 30 percentage points) of the difference in the child physical activity prevalence estimates between Scotland and England. These results will help those involved in national surveillance to determine how to increase comparability between the U.K. home nations.