For fixed sample size designs, there is a risk that expected trial outcomes may not obtain adequate power because there is usually some uncertainty about the variance of the outcome variable in the planning phase. This deficit can be remedied by reestimating the variance during the ongoing trial and modifying the initially planned sample size if necessary. From a regulatory view, any adjustment to sample size should occur without unblinding the treatment group membership of the data. Corresponding methods proposed until now are restricted to studies comparing two treatment groups. We present sample size recalculation procedures for multiarmed trials and compare their performance by Monte Carlo simulations.
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