Dear Statisticians
When building a multivariate model to test for associations between an outcome variable and multiple factors, I tend to avoid testing for a significant interactive effect between two factors if I have already found that the main effects for the corresponding factors are not statistically significant.
Nevertheless, I am conscious that there is some lack of consensus amongst statisticians as to whether this is an appropriate approach to take. I would be interested therefore to receive individual views (together with explanations) as to whether or not the above approach is justifiable.
The above issue is strongly related to the question of what to conclude if an interactive effect proves to be significant in a multivariate analysis when neither of the main effects were significant. I would therefore very much welcome some suggestions here too!
Many thanks
Best wishes
Margaret
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