Nancy was sure repeated measures was appropriate and the response led her to fear that she had grossly misunderstood a very basic tenet in her statistical training. The advisor told Nancy that actually, a repeated measures analysis was inappropriate for her data. Nancy had asked for advice about how to run a repeated measures analysis. Not too long ago, I received a call from a distressed client. The below discussion of ANCOVA and Repeated Measure ANOVA is taken from here.Īnalyzing Pre-Post Data with Repeated Measures or ANCOVA (by Karen Grace-Martin) The group and T1 regression terms are outputted in the RM ANOVA respectively as the group x time interaction and T1 x time interaction. RM ANOVA (with a covariate) asks "How does the mean difference in time points differ between groups over and above what you would expect from the T1 score". RM ANOVA: T2 - T1 = intercept + C*group + D*T1 Two common hypotheses of interest can be tested using ANCOVA and Repeated Measures ANOVA and formulated by multiple regression equations as below.ĪNCOVA asks "How do the T2 means differ between the two groups over and above what is predicted by the T1 score". L(earning) D(isabled) and General Population). Consider a design with two time points corresponding to a pre (T1) and post test score (T2) and two groups (e.g.
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