This is an age old question. It's too broad strokes to trying to generalize the answer to all admission committees (I guess they are called adcoms but I too thought that ended in medical school..lol).
Research is an interesting concept in general but here are some guidelines on how it works (and I may have reviewed some of these in previous posts). If there are any faculty out there reading this no need to become super defensive or hurt about things as this is amassed from speaking to interviewees (being one myself in the past) and speaking with those on committees (including being on them myself).
1) Not all admissions committees are the same but many (if not most in some committees) will count #s.
Most people (whether they like to admit it or not) will simply count as a first gestalt. If you have that committee member that cares about the impact factor of the journal, well I surely hope they actually read the paper but they are far and few in between. So ideally, you will be in a situation where you have mentors or a group of mentors that diversify your portfolio. It's a lot like investing because you truly are investing time when working on research projects (see below). For those that say they don't ever count, it's simply not true. Everyone counts. It just that some will actually look at the quality of the journal. But most just talk about candidate A had X number of pubs and candidate B had Y number of pubs. If you can hit double digits, it's better. Think about it: 12 sounds better than 5. I think it a bit silly but that's how it works viscerally. I've caught those that pride themselves on "looking at only Iquality" spout off the numbers when they are supporting their candidates. Bigger is better. Quality counts but that's a bit more variable from committee to committee but you bet they at least have a few people (if not the majority) on each committee that is simply counting.
2) Do you need double-digit publication numbers to match?
No. Of course not. I see people match with zero pubs too. You better be a pretty amazing interviewer though.
3) Diversify your publications and this will be a genuine way to increase your publication counts
Mentors are dime a dozen. The good ones are not. Research years are your opportunity to really focus on this so that is why those that take a research year really benefit. This is why research years are important. They serve as focused opportunities. Some students are more productive even without taking the research year. Said another way, I've seen lazy students that take the research year and get nothing accomplished and those that don't take a research year and get a ton of publications. That said, a research year is a golden opportunity to really focus on writing and publications. So what does diversification mean? It means the mentor realizes that students are taking a risk with projects but they need to make it so that the chances of succeeding are still kept high. Primary projects should be carefully designed so that they can be completed by a medical student. This is true of both clinical research and basic science research. Basic research is really tough to complete in one year regardless of planning. Clinical studies need to be focused. Publications should also include literature reviews, meta-analyses, case reports, book chapters, chart reviews so that there is some reward along the way. A good mentor will diversify these opportunities so that you stay productive along the way even if the higher risk major project takes longer than expected or does not produce results. Some people are so productive that they can get their publication counts up to 20+. I don't care whether you think this is fluff or not. If you get a student that is able to be this dedicated, many actually start to catch the bug for publishing and can develop a genuine interest in academics. Whether they stay in academics or not is "whatever" but these committees want that for the most part. You are a lot more believable about your passion for academics if you have a love for writing as shown by a track record of productivity. In my experience, students can start to develop their own mini projects and that is when you know as an interviewer that the student likely has a genuine passion. It's subtle but pretty huge in some committees. Clearly, most people do not stay in academics but these committees are still looking for people that have a love for the academic environment (unless you are interviewing at a program that clearly does not have much academic component and is clinically more heavy).
4) First author publications.
First author publications look better. It's not rocket science. But you get to list all of your publications so having middle author publications is great. My point is if you are on a collaborative team and you are helping with some publications but not as the primary person and then the primary on other projects/publications, this is yet another way to increase your productivity. Again, most committees will count and if they see a good number of first author publications (especially on complete projects), they will not care and this will actually show some level of teamwork in your ability to work with others. Some can disagree, but truth is many are simply counting (see #1).
5) Don't overlook the value of good interviewing
Yes, I realize that this thread is about publications. However, I see a lot of students think that publications will overcome bad interview skills. They do not unless you have published in major journals (PhD or otherwise) massive impact journals. This is an entirely different topic but suffice it to say that the presentation and delivery of yourself (the how) is more important than the words that you say (the what). If you have a ton of publications and come across flat, it's the highway to 10+ interviews and no match. Don't work so hard to look good on paper and forget about looking good in person. I've seen some heartbreaks in this area. Getting feedback on yourself is hard. It's can rock you to your core if a mentor tells you that you have tendencies to come across off-putting or if you come across overly intense or if you come across as nervous and flat (three examples). It's really a challenge to speak to students about this. Sometimes the mentors were not good interviewers themselves but have learned along the way and still have valuable feedback. However, a lot of students are truly incapable of having these conversations and what's in it for a mentor to have an open discussion if it's only going to lead to drama or anger. None. So if you are something that doesn't do well with feedback or having people talk to you about these things, you better get insight real soon or you might fall flat on rotations/interviews despite having all the publications in the world. With the growth of the importance of patient satisfaction, there is a greater drive to get applicants that have innate bedside manner rather than just being socially awkward with 30 publications.
Social smarts and good interviewing can make up for lower publications numbers. Publications can't make up for social awkwardness (except in some situations as I mentioned before).
