At my residency program (Med-Peds) - your interview scores (a composite score from interviewers) are weigh equally to your Step 1 score. Step 2 score also carry equal weight. Your total score (step scores, interview scores, MSPE score) will be used to generate a list, ranking highest score to lowest. We then meet to move people up or down. I've seen people get moved down on rank list when concerns about step scores are brought up (ie concern about clinical knowledge base, ability to pass THE boards). I've seen people move up the rank list despite their board scores (the person made a strong impression with the interviewers or resident, etc).
For the categorical pediatrics program, due to volume of interviewees/applicants, less individualized attention occurs when it comes to rank list - but the interview scores and step scores hold equal weight. So you may get interviewed, be well liked, but be ranked lower on the list due to low step score (which will result in lower overall score used for ranking). There's some movement on the list, but most stay in the order that the list generates.
Same with medicine.
However, that's just one university hospital (with medicine, peds, and med-peds). Other places may be different. YMMV
For some empirical data:
(from NRMP, for DO applicants, 2016 residency match)
For pediatrics, the average rank list of successful applicants for acgme peds (for DO applicants) was 9.5, with unsuccessful (matched) applicants rank list 4.8
Mean COMLEX 1 score for successful pediatrics applicants to ACGME Peds (for DO applicants) was 550 (464 for unsuccessful applicants)
Mean COMLEX 2 score for successful pediatrics applicant to ACGME Peds (for DO applicants) was 569 (462 for unsuccessful applicants)
If you ranked 14 spots, your probability of matching, based on NRMP Charting outcome, is close to 1.0
reference: Graph PD-1: Probability of U.S. Osteopathic Medical Students/Graduates Matching to Preferred Specialty by Number of Contiguous Ranks, Page 100 )
Source of above statistics
http://www.nrmp.org/wp-content/uploads/2016/09/Charting-Outcomes-US-Osteopathic-2016.pdf