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I want to calculate the number of participants I need in order to get a power of 0.95, when replicating an effect. The effect size of this effect is not reported in the previous study, which is why I want to calculate it from the $F$ value and the degrees of freedom. The ANOVA is a repeated-measures within-group 2 x 2 ANOVA.

Is the following formula adequate to calculate partial $\eta^2$?

$$\eta^2_p = \frac{F \cdot df_{\text{effect}}}{F\cdot df_{\text{effect}}+df_{\text{error}}}$$

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    $\begingroup$ Repeated-measures ANOVA with only two conditions is just the paired t-test, right? Or are there any between-subject factors or perhaps other within-subject factors? $\endgroup$
    – amoeba
    Commented Apr 9, 2017 at 19:08
  • $\begingroup$ @amoeba Thanks for the comment. I have updated the question. $\endgroup$
    – Gilfoyle
    Commented Apr 16, 2017 at 6:36

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