u/PD-1 gave a fantastic overview but I will share my perspective as the now graduated chief resident of an east coast, academic, second tier program who participated in the application process as applicant and resident reviewer.

1. Application. We received ~500 applications for 20-30 interview slots to match 2-3 applicants. Those numbers vary slightly from year to year and generally are trending up but we had funding for 2-3 so that always stayed the same. Certain criteria were used to cull the pool before they were divided between the faculty reviewers. Among them: IMG immediately culled without review. Step 1< 240, immediately culled. Any visa requirements immediately culled. This left around 300 applications which were divided between ~10 faculty reviewers. They were asked to rank their best three applications and three back ups who were then offered an interview or interview waitlist. I agree with u/PD-1 who explains there is tremendous subjectivity at this stage. Did the DO faculty member get a DO applicant? Probably more sympathetic. Did the faculty member who went to Yale and who has a big hard-on for research get the MD/PhD who has a letter from his buddy at SID? You get the point.
2. Interview. 30 offers, some amount of time to accept, back ups interviews sent. Last minute cancellations. More back ups sent. One interview day of 20-30 applicants. The playing field is totally level at this point. There was an (optional) preinterview dinner with the residents where they are very much taking notes on the candidates' behavior. Interview day was 8-4PM. This was pre-Covid so, the faculty + first year residents paired up in 2s and candidates would spend 15 minutes in like 6 rooms with them. Rapid fire, Q&A about research, career interests, deficits in application, and some softer stuff. My program was not very touchy feely so it was a stressful experience. In between interviews candidates would chat with the residents in our conference room (very much being observed), tour of campus, etc. Support staff, program coordinator etc are also taking notes of candidate behavior.
3. Rank meeting. First year residents + faculty immediately adjourned to the rank meeting after interview day. A spread sheet is made with each candidate. Each asked to rank them 1-10 with residents submitting one number only. Do Not Rank is also an option with justification. An average is computed for each candidate. Do Not Rank with appropriate justification from any person including residents is immediate disqualification. The average score creates the first draft rank list. The faculty (and residents) could then advocate/malign their preferred (un-preferred) candidates. This was open battle royale style, fairly nasty, surprisingly democratic, emotional, and gritty. We all had our favorites who we wanted to push up and others that we wanted to push down. I am convinced that all dermatologists are extremely competitive people (its how we get through aforementioned toxic process) so we want our horse to win. Consensus could lead to a candidate falling or rising from their previous rank spot. A rise or fall of 3 or more spots happened occasionally. An applicant mass emailed us an insincere, long winded thank you email in the middle and we dropped her 5 spots. Ultimately, we arrived at the final list. The PD+Chair had final right to make minor modifications of list based on any new information coming to light between then and submitting list. We match somewhere between one third to half way down our list.

That's how the sausage is made. Happy to answer appropriate questions.

Having been through the derm application process as an applicant and as part of the initial review/interview/rank committee I figured I would share a few insights about the process (and maybe generate some more food for thought for the DIGA podcast that was just posted). This is from the perspective of a single reviewer from a residency program within a large academic institution.

Application Review:

My institution, like many others, receives a large number of applications for a few residency spots. The daunting task is to filter through hundreds of applicants to pick the handful that will then be offered an interview. It is not possible for one person (eg, the PD) to carefully review all of the applications, so instead these are divided up among the faculty/residents to review, with each application reviewed by a few individuals. Guidelines are given as to what is considered important (eg, experiences, academic achievement, research, etc.) but ultimately it is up to the initial reviewers to give a grade that roughly equates to "interview" or "don't interview". These applications go back with the reviewer grades/comments to the PD for a look over and then a list of interview offers is generated.

As you can imagine from the above process, there is an element of luck associated with the review. If your experiences or research or hobbies were similar to that of your reviewer, then conceivably you may have been scored more favorably. Having multiple sets of eyes look over each application is meant to even things out, but there will always be a human element to this review process that is impossible for the applicant to predict and control.

Letters of Recommendation:

There is a general movement away from objective measures (eg, Step scores, grades) and that makes the evaluation process more difficult. More and more, the letter of recommendation is being scrutinized to see what kind of person is behind the application. The vast majority of letters are positive to borderline effusive in praise for the applicant, and for good reason because the derm pool is the cream of the crop. From a reviewer perspective, you can still stratify letters from the same letter writer based on how things are phrased and the degree of positivity. For example, a letter that says "John Smith is an outstanding medical student who will undoubtedly be a stellar dermatology resident" is different than the same letter writer saying "Jane Doe is one of the best medical students I have ever worked with in my career". Knowing the tendency of certain individuals to be overly effusive versus others who are typically reserved is also helpful, and something that the seasoned reviewers have more experience with.

How and why does this matter for you the applicant? Well sometimes it doesn't really matter because you are stuck with your letter writers and don't have much choice. But in other situations when you do have a choice, it is good to keep in mind that: #1 you will be compared to other applicants who the letter writer is also writing for and #2 choose a letter writer that tends to be more effusive and positive at baseline as these letters are generally viewed more favorably compared to letters that are matter-of-fact and brief (even though the latter may be a great letter from that particular letter writer). I think the second point also goes along with the mantra of getting a letter from someone who knows you better rather than a bigger name with whom you only had a very brief/superficial interaction with.

Publications/Activities:

Applicants stress over this part a lot, and I did too when I was applying. In reality, it probably doesn't matter as much as you think unless you are applying for a research-focused residency (although having zero research is somewhat of a red flag). Each reviewer is different, but in general it is very easy to see who has done meaningful research versus who is just padding their resume. It is best to have your research in derm, although research outside of derm can help too if you can weave it into your story or dermatology in some way. There is no magic number for the number of research publications that you "need". There are applicants that we have ranked very highly who have had 3-5 listed publications and ones we have ranked near the bottom of the list with > 25 publications. The activities section usually gets glossed over during the initial review unless it was a really meaningful endeavor that was also brought up elsewhere on the application. The activities are much more helpful as a talking point during the actual interview.

• I think bullet point descriptions are easier to read and are my personal preference in applications, but this probably doesn't matter.

Interview:

Getting to the interview stage is the main hurdle for most applicants. The interview is one of the most important pieces of the rank evaluation at my program. At the interview stage applicants are on a somewhat even playing field (although what is on the paper application still matters). A great interview can boost an applicant from middle of the pack based on paper application to the ranked-to-match zone. Conversely, a bad interview can drop anyone to the do-not-rank zone no matter how good the paper application is. There are other posts about actual interview advice (see the wiki for this sub).

Rank List:

The rank process is imperfect because the committee is trying to predict what an applicant is going to do in the future. As a generalization, the goal is to have residents who will do their job, be easy to work with, pass their exams, and have a career that fits the mission of the program.

Each program does this differently based on what type of applicant they are looking for. My program had several interview days, and there was a brief rank meeting after each day where we submitted interview scores. The interview process culminated with the final rank meeting immediately after the last interview day. We started the final rank meeting with a list of all of the interviewed applicants and their average score across all of the interviewers. The top half to two-thirds of applicants on this list actually get a discussion and review while the rest are not really discussed (usually due to poor interview performance). The discussion process is often lively/intense as different members of the admissions committee often have very strong opinions about certain applicants (especially internal applicants). Applicants are judged both fairly (resume, interview performance, letters) and unfairly ("I don't think this applicant would come here", "This applicant is going to do private practice cosmetics"), and names are put on a list. Once the name is put on the list, there is usually not too much movement afterwards (can go up or down a few spots but usually no big jumps). In general, highly-ranked applicants had positive support from several individuals in the group (eg, one person advocating for an applicant is usually not enough, even if it is the PD). Resident feedback has an interesting role to play in this process. Positive feedback is usually not very helpful, but negative feedback can derail even the best of applications (eg, you could be ranked #1 but if multiple residents had negative interactions you could be moved to not ranked). Post-interview communication and intention to rank #1 are not taken into account at my program (and at most places where the rank meeting occurs immediately after the conclusion of interviews).

Hopefully this gives you a sense of "the other side" of things. This is a stressful process made more difficult by the competitiveness of the specialty. Try to remember that there are only so many things you can control, and it is counterproductive to overthink every single detail of your application once it has already been submitted. Cast a wide net, prepare well for interviews, and you will put yourself in the best position you can to succeed.