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Table 1 Sample size and power under different scenarios

From: Randomised controlled trial of improvisational music therapy's effectiveness for children with autism spectrum disorders (TIME-A): study protocol

Raw difference on the ADOS scale (SD = 5) Standardised effect size (Cohen's d) Power at first interim look1 Test power over all 4 interim looks2
2.5 0.5 (medium effect) 93% 100%
2 0.4 76% 100%
1.5 0.3 47% 99%
1 0.2 (small effect) 20% 80%
  1. Note. Based on 10000 simulations for each scenario. 1Usable N = 235 (300 randomised). 2Maximum usable N = 939.