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Monday, March 5, 2018

Effect of Multiple Byes on Win Probability + ACC Bracket Math

In the past I've always put out win probabilities for my MDS Model for the top 5 conference tournaments. Thanks to the Big 10 moving everything up a week to play in Madison Square Garden, I completely missed it this year. So here's the bracket math for the ACC and only the ACC:



SeedTeam2nd RoundQuartersSemisFinalChampion
1Virginia100.00%100.00%84.04%70.36%49.35%
8Florida St.100.00%49.58%7.86%3.93%1.31%
9Louisville100.00%50.42%8.11%4.09%1.37%
4Clemson100.00%100.00%50.51%12.96%5.05%
5North Carolina St.100.00%60.17%25.27%5.18%1.67%
12Boston College56.39%23.97%8.36%1.37%0.36%
13Georgia Tech43.61%15.86%15.86%2.12%0.47%
2Duke100.00%100.00%72.32%52.98%26.62%
7Virginia Tech100.00%55.27%12.90%5.98%1.58%
10Notre Dame77.36%39.45%9.49%4.49%1.21%
15Pittsburgh22.64%5.28%5.28%1.13%0.12%
3Miami FL100.00%100.00%35.31%11.00%2.81%
6North Carolina100.00%70.14%44.93%19.40%7.03%
11Syracuse57.68%18.78%8.69%2.46%0.57%
14Wake Forest42.32%11.07%11.07%2.55%0.48%
Virginia is a cut above in the model, with Duke the only other serious threat. Nothing surprising there.

But this spawns a bigger question: which teams/seeds benefit from the double bye/single bye tournament format? All major conferences (including the ACC) use some iteration of this multiple bye system where the best teams get two byes (playing at most 3 games), the middle tier get one bye (playing up to 4 games), and the worst teams have to play 5 straight games (in 5 days) to win the conference title.

I've written on the short-term effect of seeding in the past, and so there needs to be a definition of what "benefits" a team. For my purposes here, I'm only looking at each team's chance of winning the tournament.

I reran the win probabilities with a standard 16-team bracket (where only the 1-seed gets a bye) and then compared this output to the current format:

SeedTeamQuartersSemisFinalChampion
1Virginia100.00%84.04%70.70%49.82%
8Florida St.49.58%7.86%3.98%1.34%
9Louisville50.42%8.11%4.14%1.40%
4Clemson70.72%43.16%11.07%4.35%
13Georgia Tech29.28%11.55%1.54%0.34%
5North Carolina St.57.50%27.79%5.69%1.85%
12Boston College42.50%17.50%2.86%0.76%
2Duke91.52%69.82%51.27%25.76%
15Pittsburgh8.48%1.95%0.42%0.05%
7Virginia Tech49.01%13.66%6.37%1.68%
10Notre Dame50.99%14.57%6.94%1.88%
3Miami FL61.30%25.59%7.90%2.02%
14Wake Forest38.70%12.16%2.75%0.51%
6North Carolina67.43%45.74%19.73%7.16%
11Syracuse32.57%16.50%4.62%1.07%
As expected, the current format:
  1. Benefits the top seeds, who have to play 1 less game (except for Virginia, which we'll get to)
  2. Is about the same for the middle seeds, who have to play the same number of games, but have a slightly higher chance of playing a worse team in their first game
  3. Damages the chances of the higher ranked worst seeds, who have to play an additional game

Champion
CurrentNo ByesDif
1Virginia49.35%49.82%-0.46%
2Duke26.62%25.76%0.86%
3Miami FL2.81%2.02%0.79%
4Clemson5.05%4.35%0.70%
5North Carolina St.1.67%1.85%-0.18%
6North Carolina7.03%7.16%-0.13%
7Virginia Tech1.58%1.68%-0.11%
8Florida St.1.31%1.34%-0.03%
9Louisville1.37%1.40%-0.03%
10Notre Dame1.21%1.88%-0.67%
11Syracuse0.57%1.07%-0.50%
12Boston College0.36%0.76%-0.40%
13Georgia Tech0.47%0.34%0.12%
14Wake Forest0.48%0.51%-0.04%
15Pittsburgh0.12%0.05%0.08%
The outlier is Virginia, which has the same number of games in each setup, yet has a worse chance of winning it all. Their first (bye) and second (Florida St/Louisville) matchups remain the same, but Duke's chances of making the final are greatly increased (which specifically hurts Virginia).

Overall, playing a different number of games has the greatest effect on the odds of winning the tournament, but matchups do also matter. This is why the very worst seeds are helped slightly and the best (Virginia) is hurt, even though they have to play 1 more and 1 less game, respectively.

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