The justification for adding a road-win bonus to the RPI is based on the premise that the home team wins 70% of college basketball games. This has been cited in nearly every article on the new RPI, and usually as a direct quote from basketball committee chairman Bob Bowlsby. This is a classic case of using stats in a misleading way. While that number is technically accurate, it is inaccurate to assume that all of those wins are due to a home-court advantage. For instance, in a large majority of non-conference games the home team also happens to be the better team, and in many cases the much better team. Did Illinois beat Maryland Eastern Shore because the game was played in Champaign?
One way to eliminate this effect is to limit the scope to conference games. This way ensures that the better team is equally at home and on the road in the sample. For all 2500+ conference games in the 2004-05 season, the home team won 62% of its games. But more to the point, let’s find out how hard it is for teams being considered for an at-large bid.
Taking teams ranked 34 through 54 in last year’s basic RPI, their difference in home and road winning percentage is striking. I chose this range because this includes teams generally considered on the bubble. It turned out in 2004, that 8 teams in this range got an at-large bid, 8 were left out, and the remaining 5 received automatic bids.
Overall these teams combined for a 89-84 (.514) record in conference road games. At home they were 135-38 (.780). It’s interesting what happens when the at-large teams are separated from the NIT teams. The 8 at-larges went 39-27 (.591) on the road while the 8 NIT teams went 23-42(.354). Their respective home records were almost identical (51-15 vs. 47-18). Road play is clearly what separates the men from the boys. For these teams, it is not so hard to win on the road.
Of those 16 teams looking for an at-large bid in the slot I looked at, only two of the eight selected (Arizona and South Carolina) did not have a winning record in conference road games. Of the eight that were not picked, only Utah State had a winning road record in conference. Utah State was regarded as the last team left out of the field.
So it seems like a good idea to include site data in the RPI, except when you consider that the committee did a great job on its own of weeding out the folks that succeeded away from home. As I said last December:
The team that does the best job, year-in year-out, of abusing the home court advantage is Hawaii. It’s really no fault of theirs because they never have to schedule non-conference road games and they usually get some decent competition to come to the islands. This year they will have to head to the mainland to play in the Bracket Buster in February. But for the other 325 teams, the distribution of game locations doesn’t make enough difference to justify making a simple formula more complicated.
These posts were motivated by a discourse between Joe Lunardi and Jeff Sagarin last year in which Sagarin attempts to promote his own super-secret formula to replace the RPI. But college basketball does not need a super-secret formula – it hasn’t worked out real well for college football.
And considering its simplicity, the RPI is pretty good at what it’s supposed to do. Winning games is good, playing a tough schedule is good. But more fundamentally, just being a good team is good. There’s really no easy way to cheat the system. And even if you could, there is a bunch of humans waiting at the end of the season to try to smooth out the problems.
Now that we know (sort-of) what the NCAA will do to adjust the RPI, just how much of a difference will it make? Was Notre Dame coach Mike Brey was right when he said,
“If we had that formula last year, we’re a seven seed.” [South Bend Tribune, 10/23/04]
Next Post: Last season’s adjusted RPI.