The last post about home court advantage by conference generated quite a bit of e-mail traffic. It was actually only three people that responded, but that represents half of my readership at this time of year. The point raised in the e-mails was that [major conference] was at a disadvantage because dominant teams at the top of the conference artificially bring the home winning percentage down by winning almost all of their road games. While I intended this post to be about why the future of possession-based stats is dependent upon Utah State winning the WAC this season, I feel duty-bound to slog through another post about the randomness of home court advantage.
Let me say first that part of the theory is sound. A team going unbeaten (or winless) will naturally drive the conference home record towards .500. However, a couple of points need to be made before we do any semi-serious analysis of this. One, this domination on the road says something about the ability to win in those road venues, and two, even the little conferences have their dominant teams. The only conference unbeatens in ’04 were from the Big West and SoCon.
To dig in further, I created a measure of parity in each conference. The Parity Index goes like this: take the standard deviation of each team’s conference wins and divide it by the length of the conference schedule.
So as an example, the 2005 Big South would be
SD(15,11,8,7,7,7,7,3)/16 = .2202
I don’t like small numbers, so I multiplied every result by 100. The Parity Index for the Big South was 22.02. It turns out this is about average among conferences. Here’s the complete list for last season…
CAA 26.96 Big Ten 26.95 Big West 25.79 Patriot League 25.61 Mountain West 25.61 MEAC 24.85 America East 24.71 Southland 24.53 Big East 24.28 SEC 23.99 Atlantic 10 22.77 WAC 22.53 SoCon 22.41 MidCon 22.32 West Coast 22.26 Big South 22.02 Sun Belt 21.76 ACC 21.10 OVC 20.92 Ivy League 20.56 Big XII 20.47 Horizon League 20.01 Conference USA 19.87 Big Sky 19.84 Pac 10 19.60 Missouri Valley 18.52 NEC 18.43 Atlantic Sun 18.03 MAC 17.27 MAAC 16.56 SWAC 14.81
The PI is a simple measure of how close each conference is to Paul Tagliabue’s utopia. If every team finished .500, the conference PI would be zero. (For the record, the 2004 NFL had a PI of 19.25.) In the SWAC’s 18 game schedule, every team had at least 5 wins and 6 losses. In the CAA, only one of the ten teams finished within 3 games of .500. The Parity Index may not be the most scientific way to do it, but it appears to be a reasonable way to measure the competitiveness of a conference.
It turns out there isn’t much connection to conference parity and home court winning percentage. The correlation between home winning percentage and parity index is negligible. The five conferences with the most parity ranked 25th, 9th, 2nd, 30th and 22nd in home court record last season. The five with the least parity ranked 23rd, 8th, 9th, 15th, and 7th. Historically, the 2003 Ivy League had the least parity since 2000, with the help of one unbeaten and one winless team among their eight. They tied for the worst home record (28-28) in 2003. The 2004 Big Sky had the most parity since 2000, with six of its eight members going 7-7 or 6-8. They finished that season third-to-last in home record.
How does this happen? Probably because that while a team running the table drags the home winning percentage towards .500, those teams in the middle can drag a winning percentage below .500.
OK, let’s move on. Now about that WAC race…