What amount of work should a well compensated research assistant put into a paper before they're included as a co-author? Is there any norm? Suppose this is a field where 1 to 3 authors on any given journal paper is the standard amount (e.g., economics/finance/econometrics).
What if they do 30% of the paper? What if the paper requires (model building, programming, writing), and each component is about 33% of the paper, and the RA does all of one of these and helps a bit with another one of these?
I would think the answer is never, unless it was an unusually large contribution or the professor was feeling nice. I think this because otherwise they would've just gotten an experienced co-author who could bring much more to the table who they also don't have to compensate with any $$.