The regular season has ended and the playoffs have begun. It would be useful to have a set of playoff grade data to do playoff probabilities, and though I’ve been down and out this season (no job at times, foot stress fracture at times, and a bad right shoulder), I currently have some time off my new job, a new laptop, and enough time to grind through some playoff numbers.
NFL stats at the end of the regular season:
To explain the columns above, Median is a median point spread, and can be used to get a feel for how good a team is without overly weighting a blowout win or blowout loss. HS is Brian Burke’s Homemade Sagarin, as implemented in Maggie Xiong’s PDL::Stats. Pred is the predicted Pythagorean expectation. The exponent for this measure is fitted to the data set itself. SOS, SRS, and MOV are the simple ranking components, analyzed via this Perl implementation. MOV is margin of victory, or point spread divided by games played. SOS is strength of schedule. SRS is the simple ranking.
Playoff Odds are calculated according to this model:
logit P = 0.668 + 0.348*(delta SOS) + 0.434*(delta Playoff Experience)
The results are given below, as a “score” in logits:
|2013 NFL Playoff Teams, C&F Playoff Model Worksheet.|
|Rank||Name||Home Field Advantage||Prev. Playoff Experience||Strength of Schedule||Total Score|
|4||Green Bay Packers||0.406||0.434||-0.842||-0.003|
|5||San Francisco 49ers||0.0||0.434||0.612||1.046|
|6||New Orleans Saints||0.0||0.0||0.658||0.658|
|5||Kansas City Chiefs||0.0||0.0||-0.602||-0.602|
|6||San Diego Chargers||0.0||0.0||-0.118||-0.118|
The total score of a particular team is used as a base. Subtract the score of the opponent and the result is the logit of the win probability for that game. You can use the inverse logit (see Wolfram Alpha to do this easily) to get the probability, and you can multiply the logit of the win probability by 7.4 to get the estimated point spread.
For the first week of the playoffs, I’ve done all this for you, in the table below. Odds are presented from the home team’s point of view.
|First Round Playoff Odds|
|Home Team||Visiting Team||Score Diff||Win Prob||Est. Point Spread|
|Philadelphia Eagles||New Orleans Saints||-0.914||0.286||-6.8|
|Green Bay Packers||SF 49ers||-1.049||0.259||-7.8|
|Cincinnati Bengals||San Diego Chargers||0.101||0.525||0.7|
|Indianapolis Colts||Kansas City Chiefs||1.650||0.839||12.2|
Some general conclusions from the data above: the teams my model favors most are the Seattle Seahawks, the Indianapolis Colts, the 49ers, the Carolina Panthers, and then the New Orleans Saints, mostly NFC teams. Since the Super Bowl itself does not have a home team, the odds change once you actually reach the Super Bowl. The sum of the SOS column and the Previous Playoff Experience column can be used to estimate odds of winning “the big one”. The strongest team in a Super Bowl setting would be the San Francisco 49ers, with a total score, less HFA, of 1.049. The Indianapolis Colts, with a total score of 0.643 less HFA, would be the strongest possible AFC contender.
A point I’d like the reader to consider is this question: should the New Orleans Saints be granted an exception to the previous playoff experience rule of “last year only counts” and given the 0.434 advantage of a playoff team? 2012 was an aberration as the coach was suspended. I’m not calculating this variation into the formula at this point, but I’ll note that this is an issue that you, the reader, need to resolve for yourself.
The road to the playoffs is not easy, a topic that can be studied by trying to calculate the path to the playoffs of the Indianapolis colts, a team that would be favored in every matchup along the way. Let’s calculate the odds of Indianapolis actually winning all three games.
|Odds of Indianapolis reaching the Super Bowl|
|WP versus Kansas City||WP versus Denver Broncos||WP versus NE Pats||Cume Probability|
Three teams from the NFC would be favored over any possible AFC contender. Those are San Francisco, Seattle, and the New Orleans Saints. Carolina would be favored over any AFC contender except the Indianapolis Colts.