Interaction analyses — How large a sample do I need? (part 3)

[This was originally posted on my blog]

Edit 5/24/21: I’ve turned the code underlying these posts into an R package: I’d recommend using this package for your own power analyses, rather than the original posted code, as it’s a lot easier to use, has more features, and I’ve fixed some minor errors.

In Part 1 I covered some aspects of what affects power for an interaction analysis, and in Part 2 I talked about interpreting interaction effect-sizes in terms…