Alpha adjustment in higher order crossover [Power / Sample Size]

posted by d_labes  – Berlin, Germany, 2018-02-01 15:01 (1880 d 10:11 ago) – Posting: # 18322
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Dear Helmut,

❝ Be aware that simultaneous comparisons inflate the Type I Error (the patient’s risk). I guess that in your first design you will not compare the two test treatments but only T1 vs. R1, T1 vs. R2, T2 vs. R1, and T2 vs. R2. With these k=4 comparisons (each performed at the nominal α 0.05) the Familywise (Type I) Error Rate will be 1–(1–α)k≤18.55%. Bonferroni’s adjusted α will be α/k or 0.0125 which translates into a 100(1–2α/k) or 97.5% two-sided confidence interval whilst keeping the FWER with 1–(1–α/k)k≤4.91% below the nominal α 0.05. The lower α will substantially increase the sample size ...

Also you may be correct I must confess that I seldom or never had done this alpha-adjustment in case I used a higher order design. Reasons:



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