The SRS for the NCAA Tournament

This post is a small a detour from finance, but I found it interesting—and it’s probably interesting to maybe five other people on the planet.

Still, I wanted to calculate the Simple Ratings System for the seeds in the NCAA Basketball Tournament. Not the teams, but the seeds.

I had no idea how to do this, but I focused on the task and eventually figured it out. I love that sense of satisfaction when you accomplish something you thought was beyond you.

First, let me explain what the Simple Ratings System (SRS) is. Well, it’s exactly that—a simple way to give a quantitative rating to a sports team based on its record. Sabermetricians have been using it for years.

Here’s the idea: Take any sports league and calculate the average per-game point differential for every team in the league. Let’s say the Orangutans have scored, on average, 5 points more than their opponents each game.

You also see that the Orangutans’ opponents score, say, 2 points more on average than their opponents. Adding two together means the Orangutans are 7 points better than average. But wait—when we plug in 7 for the Orangutans’ margin of victory, that changes all the numbers for their opponents, and that comes back and changes all the numbers for the Orangutans. This loop will repeat itself again and again and again. Eventually, though, the numbers stop changing and you have your results. (This is what I was trying so hard to figure out.)

I wanted to calculate the SRS for the seeds of the NCAA Basketball Tournament. I took all the games of the last 30 years which is when it expanded to 64 teams. Since every team but one is knocked out, each year has 63 games. I didn’t include the play-in games since those are match-ups of same seeds. I also took out later games where same seeds met. There were 21 games like that and it only happens in the Semi-Finals or Finals.

Here’s what I got:

Seed MOV SOS SRS
1 12.08 -4.03 8.05
2 7.13 -1.96 5.17
3 5.23 -1.65 3.59
4 3.48 -1.57 1.90
5 0.97 -0.10 0.87
6 0.43 0.32 0.74
7 -0.54 0.89 0.35
8 -3.18 0.74 -2.44
9 -4.29 1.11 -3.18
10 -3.12 1.50 -1.62
11 -3.94 1.63 -2.30
12 -4.37 1.29 -3.08
13 -9.13 1.54 -7.59
14 -11.04 3.07 -7.97
15 -16.10 4.83 -11.27
16 -24.51 8.05 -16.46

The chart shows each seed, their Margin of Victory, their Strength of Schedule and their Simple Rating System. The first two add up to the third.

I thought this was an interesting exercise because the NCAA Tournament is specifically designed to have an unbalanced Strength of Schedule. The best teams play the worst. The #1 Seeds are supposed to be the best, and they are.

A few things to notice. After 30 years, a #16 has never beaten a #1. They’re 0-120. As a result, the #1 Seed’s SRS is the same as the #16 Seed’s SOS.

The SRS numbers are ranked in order except for the #8 and #9 Seeds. Those are lower than you would expect (#9 currently leads #8 in the First Round, 61 wins to 59). I assume that’s from being in the lucky position of getting to be the punching bag for the #1 Seed. The #1 Seed is 104-16 in Round 2. I would think the high Strength of Schedule would have corrected for that, but apparently not. I can’t say for sure.

The table also shows something I’ve suspected for a long time — that there isn’t much difference among the middle 8 teams (Seeds #5 to #12). There’s some difference, but not a lot. A game with an expected difference of 3 or 4 points will seem awfully close. Seeds #11 and #12 both have respectable records in the First Round. They’re worth a lot of points on the brackets, but it’s not much of an upset.

(This was my first time trying this, so if any experienced hand spots some mistakes, please let me know.)

Posted by on February 24th, 2015 at 11:57 pm


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