Figure 2.

Sample size in clusters-per-arm for a main trial calculated for small and medium estimated intra-cluster correlation (ICCs) of $\hat{\rho }=0.01$ (top), $\hat{\rho }=0.1$ (bottom) and medium effect size (d = 0.25), using each method of estimating imprecision in the ICC. Plots show sample size accounting for imprecision in the ICC estimate from a pilot trial with two clusters-per-arm (green), four clusters-per-arm (blue), eight clusters-per-arm (red) and without accounting for imprecision (black). Main trial cluster size is fixed at m_f = 20.