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There are a number of questions posted by new users asking how to interpret basic linear model output with interactions. An example from just now: One main effect is positive while other is negative but interaction effect is positive in an interaction;Interpretation help.

Do we have a canonical question & answer that addresses these? If not, I can write one that explains this graphically.

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I don't know that we have a perfectly pure thread that would be considered canonical. That's especially true for 3-way interactions. You can sort the questions returned by searching on and by votes or frequency of linking to see if there's something you like. Personally, I tend to link to Interpretation of interaction term in conjunction with Interpretation of betas when there are multiple categorical variables, but note that (a) these only pertain to a 2-way interaction, and (b) I wrote both of those answers. Another of my answers I sometimes link to is the top portion of Interaction in generalized linear model. Again, partly I'm more familiar with those because I wrote them. Assuming someone actually goes to all three places and reads all of the answers, I think they could get a reasonable grasp of the idea, but then again, people may not do that and it wouldn't hurt to have all the information in a general form in one place. So a canonical thread isn't a bad idea.

I suspect that also trying to adequately cover 3-way interactions will be difficult and make the answer pretty long, though. You'll also need to consider if you want to work through the distinction between categorical and continuous variables in an interaction.

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    $\begingroup$ Thanks! I'll take a close look at those and consider how best to frame a usefully different question & answer. $\endgroup$ – mkt Jul 19 at 8:16
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    $\begingroup$ There is also quite a nice one about continuous by continuous interactions stats.stackexchange.com/questions/4964/… with some graphical aids. $\endgroup$ – mdewey Jul 19 at 13:05
  • $\begingroup$ @mdewey Thanks for that link $\endgroup$ – mkt Jul 20 at 14:57

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