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. 2021 Sep 3;30(11):2459–2470. doi: 10.1177/09622802211037073

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© The Author(s) 2021

This article is distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 License (https://creativecommons.org/licenses/by-nc/4.0/) which permits non-commercial use, reproduction and distribution of the work without further permission provided the original work is attributed as specified on the SAGE and Open Access page (https://us.sagepub.com/en-us/nam/open-access-at-sage).

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Figure 1. — Sample size in clusters-per-arm for a main trial calculated for small and medium estimated intra-cluster correlation (ICCs) of $\hat{ρ} = 0.01$ (top), $\hat{ρ} = 0.1$ (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 and pilot trial cluster sizes are assumed to be equal.