This article on this topic is fascinating. I guess I shouldn’t be surprised at how poor the research is on this topic. I wish there were more recent books by Steve McConnell, as his books on programming always seemed to include references to actual research. Then again, now I’m wondering how good that research was, although I’d still bet on McConnell’s books. I particularly enjoyed Rapid Development and Code Complete, although Software Estimation is also very good. Oh wait, doing a search, I see he wrote a book published in 2019 on agile. Hmmmm….I may have to give it a read.