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Table 2 Sample size scenarios based on differing assumptions

From: The Healthy Lifestyles Programme (HeLP), a novel school-based intervention to prevent obesity in school children: study protocol for a randomised controlled trial

  ICC Within person correlation coefficient Attrition rate Effect size detectable
     Number of SD units Difference in BMI SDSa
Base case 0.02 0.8 20% 0.19 0.25
Vary ICC 0 0.8 20% 0.14 0.18
0.02 0.8 20% 0.19 0.25
0.05 0.8 20% 0.25 0.32
Vary correlation between baseline and 24 months BMI SDS 0.02 0.75 20% 0.21 0.27
0.02 0.8 20% 0.19 0.25
0.02 0.85 20% 0.17 0.22
0.02 0.9 20% 0.14 0.18
Vary attrition rate 0.02 0.8 10% 0.18 0.23
0.02 0.8 20% 0.19 0.25
0.02 0.8 30% 0.20 0.26
  1. aBetween-group difference in BMI SDS at 24-month follow-up.