Monday, October 15, 2012

NFL Rankings - Projected Wins

There is a new feature added to my daily NFL team rankings. Building off of a suggestion from commenter Ben Moore on my MLB rankings, there is now a column labeled "Projected Wins". With each day's rankings, I also simulate the remainder of the regular season (10,000 times) and display the following:

  • Average Projected Wins - This is the average projected regular season wins, based on my 10,000 simulation runs.  This only simulates future games (wins in-hand are taken as a given).
  • Projected Win Ranking - How that team's projected wins compares to the rest of the league
  • Projected Win Distribution - On the far right is a bar graph displaying the team's projected win distribution, once again summarized from my 10,000 run simulation. The scale is identical for each team, with the x-axis varying from 0 wins to 16 wins for each team.  This can be viewed as an application of Edward Tufte's concept of small multiples.
I simulate the season as follows:

For all future games in which the point spread has not been released, I calculate the expected point spread using my GPF rankings*.  I then convert the point spread for each game into a probability according to the following formula:

  • Win Probability = 1 / (1 + e^(point_spread/7))

Where a negative point spread indicates the team you're calculating the probability for is favored.

As mentioned, this is only a regular season projection, and a relatively simple one at that.  For something considerably more sophisticated, look to Chris Cox's NFL-Forecast tool.

* How to calculate a point spread for any matchup:

Point Spread (given to home team) = -2.5 - (GPFhome - GPFaway)

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