Timeline for Can a main effect coupled with an interaction, answer my question?
Current License: CC BY-SA 4.0
7 events
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| May 6, 2022 at 18:26 | comment | added | EdM | The "main effects" are meaningful; it's just that their values depend on how interacting predictors are coded and thus they aren't uniquely defined. For any model and its specific predictor coding , however, the "main effects" are meaningful in the context of that model. They are needed to do the types of comparisons/contrasts that you need. I second the recommendation of @dipetkov that you look into the emmeans package; once you get the hang of it it makes post-hoc comparisons pretty simple. | |
| May 5, 2022 at 13:20 | comment | added | dipetkov | You might also be interested in learning about contrasts (ie comparisons), which you can do easily in R with the emmeans packages. It has lots of vignettes as well. | |
| May 5, 2022 at 12:09 | comment | added | ERMM | Thank you for your answer as well ! I understand that, I just added this link as a way to show that in some cases main effect can be intersting coupled with interactions. I was assuming this could be the case for my question as well (a different case). I still don't quit understand why this pattern of result that I expect could not be shown via the interaction + main effect since that is what is seen in the graph. But from what I gather from the responses to this post, it might not be accurate. | |
| May 5, 2022 at 6:32 | comment | added | dipetkov | If you read the post again, they argue that the main effect is meaningful when one group's mean is always higher than the other group's mean. For every value on the x-axis. | |
| May 5, 2022 at 6:31 | comment | added | dipetkov | In your plot the green and blue lines cross. In the linked post, this is just as the case "When interactions do make main effects nonsensical", and not as the case "When interactions don’t affect main effects". | |
| S May 4, 2022 at 15:31 | review | First answers | |||
| May 4, 2022 at 16:46 | |||||
| S May 4, 2022 at 15:31 | history | answered | ERMM | CC BY-SA 4.0 |