To complete “Championship Week” at Skeptical Sports, I thought I’d post a little fun research I did before this year’s Super Bowl.
Like basketball, teams with championship-winning experience outperform their regular-season records in the playoffs, especially if they make it to the Super Bowl.
So, a bit like my 5-by-5 model, I wanted to come up with a simple metric for picking the Super Bowl winner. Unlike its NBA cousin, however, this method only applies to the championship game, not to the entire playoffs. The main question is, how much better does a team with more Super Bowl winning experience do than it’s opponent?
I feel bad about my text/graphs ratio this week, so I thought I’d tell this story in pictures. Before testing the question, we need to pick the best time period. So, for what number of years does the metric “pick the team with the most super bowl wins” most often pick the ultimate winner:
This was a little surprising to me already: I thought for sure the best n would be a small number, but it turns out to be 6.
Counting 2012, there have been 26 Super Bowls where one team has won more championships in the previous 6 years than the other. Of those games, the team with the greater number has won 20, or 77% of the time—including the Giants. [True story: I was going to publish something on this research before this year’s Super Bowl, but, knowing that it predicted a New York win against the heavily favored Patriots, I chickened out.]
Of course, I’m sure most of you are just itching to pounce right now: Clearly the team with the most recent Super Bowl wins is usually going to be better, right? So clearly this must be confounding this result. So let’s compare it to the predictive accuracy of SRS (Simple Rating System, aka “Margin of Victory adjusted for Strength of Schedule”):
Looking at all 46 Super Bowls, the team with the higher SRS has won 26, or 57%. In Super Bowls where no team had more Super Bowl wins, SRS performs slightly better, correctly picking 12/20 (60%). But the real story is in the games where both had something to say: When SRS and L6 agreed, the team they both picked won 11/14 (79%). But when SRS and L6 disagreed—in other words, where one team had a higher SRS, but the other had more Super Bowl wins in the previous 6 years—the team with the paper qualifications lost to the team with the championship experience 9 of 12 times (75%).
Now, your next thought might be that the years when L6 trumped SRS were probably the years when the teams were very close. But you’d be wrong:
The average SRS difference in 9 years where the L6 team won is actually higher than in the 3 years when it lost!
So how much does L6 add overall? Well, let’s first create a simple method, a bit like 5-by-5:
- If one team has more Super Bowl wins in the previous 6 years, pick them.
- Otherwise, pick the team with the best SRS.
Following this method, you would correctly pick 32 of the 46 Super Bowls (70%), for a 10% improvement overall, despite step 1 only even applying in about half of the games (also, note that if you just picked randomly in the 20 Super Bowls where L6 doesn’t apply, you would still be expected to get 30 right overall).
Finally, to try to quantify the difference in predictive value between the two measures, I plugged them both into a logistic regression:
As you can see, L6 is much more predictive, though the 95% confidence intervals do overlap. (Though I should also note, this last chart is based on the regression I ran prior to this year’s game, which ended up being another victory for the championship experience side.)