The SPI, revisited

Retooling the ratings metric of the future.

Since I last wrote, I've done a substantial retooling of the Sam Power Index (SPI). The previous metric was essentially a product of the team's RPI rating, their strength of schedule, and their scoring differential. I realized, however, that this isn't the best way to go about it. For one thing, the RPI is a metric determined by a team's strength of schedule. Including that factor twice doesn't make much sense. Second, I realized that I was unfairly punishing teams that did poorly earlier in the season, but came alive down the stretch. A team being outscored by an average of seven points throughout the season but winning their last ten games by an average of fifteen points will be a lot more dangerous than their original record might indicate.

So I overhauled the metric, and my Excel spreadsheet now has close to four times as much data on it. I weighted in each team's strength of schedule and scoring differential for the last ten games, and I found some remarkable differences in the rankings. Even better, now that the official seedings have been released, I can compare what the NCAA selection committee and the SPI came up with. Here are the major differences:

Davidson. The Wildcats went 26-6 this year, winning their last 22 games. They're outscoring their opponents by over fifteen points a game, and outscored their last ten opponents by nearly twenty points a game. Yet the NCAA dropped them to a 10 seed for playing in the fairly soft Southern Conference and for not finishing ambitious nonconference opponents like Duke. The SPI has them listed at #4. This is one of the teams that is going to surprise a lot of people.

Georgetown. They rolled through the incredibly deep Big East conference this year, only losing to Pittsburgh in the conference final. They have a scoring differential of 11.5 points and a record of 25-4, earning them the 2 seed in the Midwest region. The SPI puts them at #20 overall, however, since they slowed down in the stretch. Their scoring differential fell to 5.6 points during their last ten games against a schedule that was only marginally more difficult than the rest of their season. The Hoyas aren't a bad team, but they aren't the dominant force everyone thinks they are. They aren't even the top-rated team from the Big East - Marquette (10), Louisville (11), and West Virginia (15) all finished higher.

Western Kentucky. Remember how I said this was the team to watch last time? Their SPI actually rose when I retooled it. They're rated at #14, which, for comparison, is only just below Texas. This is a team that beat their (admittedly weak) last ten opponents by nearly 15 points a game. That's pretty impressive, even for the Sun Belt Conference. Their first two opponents are lower in the SPI (#16 Drake and #24 Connecticut), so don't be surprised if you see the 12th-seeded Hilltoppers in the Sweet Sixteen.

Marquette. Here's a team that hasn't generated much attention this year. The Golden Eagles play in the insanely talented Big East, so they've been overshadowed by teams like Georgetown, Notre Dame, and Louisville all year. Yet they have close to the top scoring differential in the conference at 12.7 on the season. That fell to 11.5 in their last ten games, but that was higher than anyone else in the conference came up with. Even though the NCAA stuck them with a 6 seed, they have the advantage of playing in a soft region. They draw #60 Kentucky (an 11 seed) in the first round and overrated Stanford in the second (3 seed, #27 SPI). They have the guns to get past #13 Texas and even #3 Memphis, I think. Marquette's SPI is nearly three and a half points lower than Memphis', but the benefits of playing in the Big East will have them ready for such a big game. Marquette will be the surprise of the tournament.

I'm ready to predict the play-in game, for those of you looking for proof that this metric will work. The opening round game pits 16a Mount Saint Mary's against 16b Coppin State. These games are usually a toss-up when filling out brackets, but I feel pretty comfortable going to Mount Saint Mary's. Coppin State has had an amazing comeback from a 4-19 start (they finished the season on a 15-1 run) and had a 9.2 scoring differential in their last ten games, but their SPI is only 97.3570 compared to Mount Saint Mary's 103.8015. The fact is that Mount Saint Mary's has been playing all season at the level Coppin State has over the last ten games, and against similar competition. Go ahead and fill that in your bracket in pen.

I'll be posting regular updates as the tournament progresses. Feel free be amazed when I correctly pick all 64 games or mock me mercilessly when I get them all wrong.