[R-sig-ME] logistic regression on posttest (0, 1) with pretest(0, 1)*Group(Treatment, Ctrl) interaction

[Souheyla GHEBGHOUB]

Dear Rene, and any member of the list who is willing to read this : )

I have decided to use the interesting model that you have structured for me,
To refresh your memory here is what you said :

*Anyway, there is a second possibility to define your model, depending on
> how you want to interpret it. In the previous model you can say something
> about the type-of-change likelihoods depending on the treatment group.
> But you could implement the model as binomial as well (i.e. logistic
> regression) mod2 <- brm(posttest ~ pretest*Group + (1|Subject) +
> (1+Group|Word),...)  And what you would expect here would be an interaction
> between pre-test and Group. For instance; if pretest=0 & treatment 1 then
> posttest larger than with pretest=0 & treatment 2; but not when pretest=1
> (because this is a plausible no gain situation). And so on...*


But I found the interpretation of the Pretest*Group interaction results to
be tough. I still can't grasp how to claim there is an effect of Group on
posttest outcome when considering pretest. The pretest slope does not come
with 0 or 1 in the output, the Group does come with one category, but its
confusing what the intercept and slope estimates refer to in this case?

Thank you very much,
Souheyla

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