it was mixed for me, some had a pre-interview social event of some sort, others did not. i'm a guy, and for most of these i wore khakis or pants with a dress shirt, no tie. jacket was for warmth, not fashion. i saw ladies dressing most often in skirts or pants and a nice blouse, but usually not the type of business suit you see female residency applicants wearing. unless you are a super sharp dresser, you don't want anyone noticing your attire one way or the other. go with this type of classic, simple attire and no one will, rather they will or won't remember you based on the quality and quantity of your interactions. and make no mistake, the pre-interview dinner does matter.