Here is a 'scorecard' by conference for 1993, the first year I kept these data. I thought this might be useful info since the regionals are a major source of inter-conference and inter-region play that helps determine the relative strength and hence future seedings of teams from various regions and conferences.
Here is the 'histogram' of the success rate for the 1993 NCAA regionals.
------ wins ------
Conference Number 0 1 2 3 champ my comments
========== ====== === === === === ===== -----------------
SEC 6 2 3 1 big 1 + overrated 5
ACC 5 4 1 balance but no winner
Pac-10 4 1 2 1 strong showing
SWC 3 1 2 big 2 + Texas Tech?
WAC 3 1 1 1 good show
Big-8 2 2 looks underrated
Big-West 2 1 1 california is in
Big-East 2 1 1
Big-10 2 1 1
Sun Belt 2 1 1
Big-South 2 1 1
Colonial 2 1 1
Metro 2 2 pretty lame showing
Mo-Valley 1 1 shocking ;-)
Midwest Coll. 1 1
West Coast 1 1
Southern 1 1
Atlantic 10 1 1
Southland 1 1
ECAC 1 1
Trans America 1 1
Ivy 1 1
N. Atlantic 1 1
Miami(FL)-ind 1 1 Fraser-less
Mid-Continent 0 -left out
MEAC 0 -left out
Ohio Valley 0 -left out
SWAC 0 -left out
Great Midwest 0 --ignored
Play-in series started in 1994.
The ECAC appears to have started to split up in 1993, anticipating the change in how conference bids would be handed out. The North Atlantic was once part of the ECAC, but was listed as having an automatic bid. The ECAC automatic qualifier was the Patriot champ; other conferences that were part of the ECAC but had no teams in the tournament were Diamond (now gone), Metro Atlantic, and Northeast.
The Great Midwest eventually (in 1996) helped form Conference USA after struggling as a 4-team conference (too small for NCAA ranking).