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I am running a study looking at the effect of Vitamin C on muscle function. For my study design, I had 2 groups: A treatment (vit C) and a control (no treatment) group. Pre and post measurements were taken for Muscle function, and I was wondering what is the best statistical test to perform? Subjects were randomly assigned to either group.

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A 2x2 mixed analysis of variance would probably work well, assuming your muscle function outcome variable is continuous. Your experimental variable would be your between subjects factor and your pre-/post- measurements of muscle function would be your within subject factor.

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  • $\begingroup$ Ok thanks, yes, the muscle function outcome variable is continuous. Would a paired t-test work in this case as well, or is the fact that there are different subjects in the two groups makes the paired t-test an unappropriate statistical test in this instance? $\endgroup$
    – Connor3351
    Mar 27, 2015 at 16:37
  • $\begingroup$ No, not to answer the question you want to answer. A paired t-test would only allow you to test whether muscle function changes from pre-to-post, irrespective of your participants' experimentally assigned Vitamin C condition. A 2x2 mixed ANOVA, alternatively, will allow you to examine whether your two experimental conditions are different at either pre- and/or post-muscle function measurement. Presumably you are anticipating differences between conditions at the post-test assessment. $\endgroup$
    – jsakaluk
    Mar 27, 2015 at 16:50
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    $\begingroup$ Oh, ok. Yes, I'm expecting the Vit C group muscle function post-test assessment results to be different to the placebo group. What would be done in the case of non normally distributed results? Can a 2x2 mixed ANOVA still be run? $\endgroup$
    – Connor3351
    Mar 27, 2015 at 17:06
  • $\begingroup$ It depends how non-normal the distribution of your response variable is--ANOVA is robust to some violations of assumptions (e.g., normality). You should check your skewness/kurtosis statistics of your response variable. Also, are your treatment group sizes relatively equal? Unequal cell sizes exacerbate the severity of assumption violations. $\endgroup$
    – jsakaluk
    Mar 27, 2015 at 17:09
  • $\begingroup$ So the response variable is the muscle funtion in this case, right? Regarding the treatment group sizes, both groups contain almost the same amount of participants. $\endgroup$
    – Connor3351
    Mar 27, 2015 at 17:21

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