I have conducted a naming experiment for which response time was the outcome measure. There were 2 groups (treatment v control) and 3 testing conditions (A, B and C). I ran a mixed 2 x 3 repeated measures Anova with Group as the between subjects factor and Condition as the within subjects factor. There was a significant main effect of Condition, F(2, 86) = 70.99, MSE = 477,817, p <.001, η² partial = .62, as well as an interaction between Condition and Group, F(2, 86) = 15.31, MSE = [SPSS didn’t give... another problem for another time], p <.001, η² partial= .26.

I wish now to run comparisons and, whilst trying to work out whether it makes more sense to run planned comparisons or post hoc tests, I wondered whether it would be acceptable to run both: planned contrasts based on my predictions (below), and then post hoc tests on the remaining, untested contrasts - or if I should just pick one type.

Predictions:

Treatment group: Condition B > both A & C

Control group: no difference between B & A

(I was sort of agnostic about how C (a 'neutral' condition) would compare to the other conditions, except with respect to the prediction that B would be slower than both A and C for the treatment group.)

Other comparisons of interest, based on results

- both groups: C < A & B

Result Plot:

Many thanks in advance!