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Table 7 Updated sample size calculations for the adult outcomes using the between-cluster coefficient of variation from the baseline survey (with missing responses multiply imputed)

From: The Well London program - a cluster randomized trial of community engagement for improving health behaviors and mental wellbeing: baseline survey results

Outcome Baseline prevalence or mean (across all intervention and control clusters) Km Minimum detectable effect size Expected effect size in original study design
Adults     
Healthy eating 37% of adults eating at least five portions of fruit and vegetables per day 0.14 22% increase in prevalence 50% increase in prevalence
Physical activity 60% of adults doing at least five sessions of 30 min of moderate intensity physical activity per week 0.14 19% increase in prevalence 70% increase in prevalenceb
Mental health and wellbeing 18% of adults reporting feeling anxious or depressed 0.30 35% decrease in prevalence -
  16% of adults reporting consulting their GP for emotional problems (anxiety and depression) in previous 12 months 0.23 41% decrease in prevalence -
  Mean Hope Scale score = 4.6 (range, 1 to 6, higher score indicates better mental wellbeing) 0.03 Increase of 0.2 standard deviations -
  1. aEffect sizes for binary outcomes are relative increases in prevalence.
  2. aCalculations are based on multiply imputed datasets; comparison to complete cases showed no substantial differences except in Km for adolescent fruit consumption which decreased from 0.05 to 0.004.
  3. bBased on an expected baseline prevalence of 18%.