Sunday the Philadelphia Eagles return from their three-game road trip for a two-game home stand. Unfortunately, home has not been such a welcome place for these Eagles. The last time the Eagles won at home was September 30, 2012 against the New York Giants when Alex Henery kicked a 26 yard field goal with less than two minutes remaining, and Lawrence Tynes missed a 54 yarder with 10 seconds left to seal the 19-17 win for the Birds. To put this into some personal perspective, my one-year old son wasn’t born yet… he’s never seen a home win!
Last week’s simulation successfully projected a Philadelphia Eagles’ victory over the Tampa Bay Buccaneers. They won with a Nick Foles-led offense that operated at 83% efficiency (14 percentage points above their average) and a defense that held the Bucs offense to just 66% efficiency (albeit two percentage points above their season’s average). Under these circumstances, the simulation projected a nine-point Eagles win, compared to the actual eleven point margin of victory.
This week’s simulation is less clear. Through six games, the Dallas Cowboys’ offense has operated at 74% efficiency, slightly more than the Eagles’ offense, which has operated at an overall 71% clip. This, paired with the historical performances of home and away teams, lends itself to a tightly contested matchup, illustrated by the model.
After 10,000 simulation runs, the Eagles lose a small majority of the time (48.9%) by an average of just 0.3 points. If turnovers are equal for the two teams, the odds still slightly favor Dallas, but the average scores are equal (21.4). However, the Eagles can win under the following circumstances:
- By managing one more takeaway than the Cowboys, the odds of the Eagles winning increases dramatically to 74.5%.
- By operating their offense at least at their season average (71%), and keeping Tony Romo and the Cowboys offense under theirs (74%), the Eagles odds of winning increases to 87.8%. (In contrast, if the Cowboys operate at or above their average level of efficiency, and keep the Eagles below theirs, they have a 92.4% chance of winning).
The stakes for this divisional game are obviously high. First-place is on the line, tie-breakers need to be gained, the Eagles (and Chip Kelly in particular) need to win at home, and Cowboys simply need to be beaten to a pulp. It’s expected to be close, but we have a secret weapon… "Vick Foles". And my feeling is, my son will see a home win at the Linc this Sunday. Interact with the graphic to see more...
Note: NFL simulations are far from an exact science. They attempt to mathematically project the future based on history and past performance, but they can’t account for everything. A stiff breeze, a tipped ball, a freak injury, a rolling fog bank, an ol’ coach’s return, or simply a change in player attitude can alter results in a large way. Instead, simulations give us a blurry view of a series of possibilities among an infinite number of potential realities. But they’re fun. If you believe in parallel or multiple universes, then one of these simulated results could possibly occur.
The simulation is based on my home field advantage (HFA) research, which shows how there have been small but distinct and different offensive efficiency behaviors between home teams and away teams in the NFL. And not surprisingly, turnovers play a large role in equalizing the playing field. Offensive performances throughout the season were entered into a logistic regression formula born from the HFA research, and randomized according to standard error values and turnover differential.
Step 1: Calculate Offensive Efficiency (OE). I used Chip Kelly’s definition for this:
(Rushes + Completions) / (Total Off Plays + Offensive Penalties)
If you check out the HFA research, there’s a really strong correlation between offensive efficiency and team success.
Step 2: Calculate Win Probabilities using the logistic regression formula that correlated OE to team success. Here’s the formula:
Win Probability = 1 / (1 + e^-((A*OE+error value) + (B*Turnover Diff + error value) + C)), where A, B, and C are constants.
Step 3: Convert the results from Step 2 into points using a linear formula:
Points = A*(Win Probability for Eagles) + B*(Win probability for Opponent) + C, where A, B, and C are constants.