Researchers used a cluster randomised controlled trial design to assess the effectiveness of a multicomponent physical activity programme on the physical and psychological health of young schoolchildren.1 For each child, the skinfold thickness was measured at four places (triceps, biceps, subscapular, and suprailiacal), and the measurements were added together to provide a marker of obesity.

At the end of the study period of one school year, the intervention group (n=297) had a mean skinfold thickness of 32.50 mm (SEM=0.85 mm), compared with 33.70 mm (SEM=1.20 mm) in the control group (n=205). SEM, sometimes shortened to SE, is the abbreviation for standard error of the …