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Table 2 Comparison of the simulation-based approach with the analytical formulae of HH. The cells in the table are the estimated number of clusters as a function of the ICC and outcome type (continuous, binary and rate) to obtain 80 % power

From: Sample size calculation for a stepped wedge trial

ICC Analytical power based on HH Simulation-based calculations
  K=20,J=6 K=20,J=6
Continuous outcomea
0 9 9
0.1 13 13
0.2 14 13
0.3 14 14
0.4 14 14
0.5 14 14
Binary outcomeb
0 11 15
0.1 17 16
0.2 18 17
0.3 18 18
0.4 18 18
0.5 18 18
Count outcomec
0 8 8
0.1 13 12
0.2 13 12
0.3 13 12
0.4 13 11
0.5 13 11
  1. aIntervention effect = −0.3785; σ e =1.55.
  2. bBaseline outcome probability = 0.26; OR = 0.56.
  3. cBaseline outcome rate = 1.5; RR = 0.8.
  4. Notation: K= number of subjects per cluster; J= total number of time points, including one baseline