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I'm currently working on our thesis and I got stuck with the analysis part for I am not sure which statistical test I should use. My work had 5 groups. 1 positive and 1 negative control and 3 experimental groups. Is it right to use a 2-way ANOVA? And should the controls be included in the ANOVA? I'd like to compare if the experimental groups significantly varied from the control groups. What would be the best fitting test? Thank you so much.

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From what you say so far it sounds like a one way ANOVA because you have mentioned only one independent variable: Group. This would have 5 levels. If you have other variables, that would add to the "ways".

You should definitely include the control group, otherwise you will not be able to compare them to the treatment. You can test your hypothesis with a contrast.

As for "best fitting test" that's impossible to say without looking at the data and the results of the models.

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  • $\begingroup$ Thank you! :) But what if I included a pretest and a posttest? $\endgroup$ – user36774 Jan 2 '14 at 10:10
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    $\begingroup$ Then there are a number of choices: Gain scores, ANCOVA or possibly mixed models. $\endgroup$ – Peter Flom Jan 2 '14 at 11:38
  • $\begingroup$ Why not a repeated measures ANOVA? $\endgroup$ – Behacad Jan 31 '14 at 19:01
  • $\begingroup$ RM ANOVA makes assumptions that mixed (or multilevel) do not. See e.g Hedeker & Gibbons, Longitudinal Data Analysis $\endgroup$ – Peter Flom Jan 31 '14 at 22:10

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