i disagree, i think research as a 4th year can be more useful than during residency cause you have time to do it right. nobody expects an intern to publish, and your application goes out in November of your R2 year, that's not a lot of time to make a meaningful dent in a project, especially if you get a bunch of call months early in your R2 year. The whole point of research in residency is to get a faculty member to support you w/ LOR's and phone calls. You won't be making any real contributions until your R3 year, and by then you will have already matched at a fellowship (hopefully). Most importantly, it tells your own program if you will be willing to do research as a fellow, which is invariably what they want. I say publish while you can, it all looks the same on paper no matter when you do it. And 4th year gives you ample time to do research, most schools will even give you 1-2 months of elective credit for a research project.