A sample of patients will undergo two treatments. Every patient will receive both treatments.One treatment will on the left side and the other different treatment on the right side. Repeated measurements will be done for each side at several time intervals.

My questions are:

  1. Which analysis is appropriate for that case. Two-way ANOVA with treatment and time being the factors, or simply a repeated measures ANOVA because of the two sides dependency.

  2. If it's the latter test, for sample size calculation, should I use in Gpower the ANOVA: repeated measures,within-between interaction option

  3. If it's the two-way ANOVA, how to calculate the sample size for that? Any software?


For your third question, GPOWER (current version) permits one and two-tailed tests as an option.

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    $\begingroup$ Can you say more here & address the other questions? This is more of a comment than an answer by our standards. $\endgroup$ – gung - Reinstate Monica Dec 16 '15 at 15:34

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