I have a simple multiple choice question in a REDCap instrument where I want respondents to be able to only select one of the first three options, but also a fourth option that can also be selected.

For example, using the following multiple choice options, they can check 1 and 4, 2 and 4, or 3 and 4 — but never 1, 2, and 3 together:

1, A
2, B
3, C
4, Estimated

I’ve tried using a combination of @IF, @MAXCHOICE, and @NONEOFTHEABOVE action tags, but my understanding is they (action tags) only evaluate when the survey or data entry form is first loaded (i.e. not dynamic). @MAXCHOICE = 2 helps limit the number of selections, but it can’t further delineate between the two sets of questions.

*One workaround I know of would be to split the question into separate fields, which would work perfectly fine, but I’m hoping to find a solution that works with all included in a single field.