# Sample size required for mixed design ANOVA to achieve adequate statistical power

### Context

I ran an experiment with 3 x 2 design with three levels of within subjects factor (repeated measures) and two levels to the between subjects factors.

I am interested in examining the changes from baseline and the interaction effect.

### Question

• How do I compute the required sample size for a 3 x 2 design in order to achieve adequate statistical power?
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You say that you have "ran an experiment" and you say " how to go about computing sample size". The short answer is "count your number of participants". But I assume you intended to ask "what sample size is required in order to achieve a given (perhaps "acceptable") statistical power. I'll edit your question to reflect this; feel free to modify if I have misconstrued. – Jeromy Anglim May 4 '11 at 4:01

• Download this free software and go to the tests - means - Repeated Measures ... menu.
• The software permits a priori (i.e., calculate sample size for given effect size, alpha, power, and design) or post hoc (i.e., calculate power for given sample size, effect size, alpha, and design) power analysis.