by Bruce D
There are many win probability tables published each week for upcoming NFL games that calculate the percentage chance of each team to win versus another. Perhaps the best known to visitors of Advanced NFL Stats is the weekly probabilities at The Fifth Down.
I've seen several comments about these types of probability charts asking how the win probability percentage equates to points(margin of victory). I've yet to find a reply to any of these, so I did some analysis in this regard using data for the last 6 NFL seasons, 2004-2009.
This analysis used points based on completed games by adding various points to each team's score, and then calculating the percentage of the games a team would win if given the extra points.
For each number of points tracked(VariablePoints, seen below) the following was performed for every team/game combination for the last 6 seasons.
If (points for + VariablePoints)-(points against) > 0, then its a win, and all wins are counted(win count).
Then to get the average:
(win count)/(number of team/game combinations checked, eliminating any ties)
The following table will show the actual win% based on the variable points.
So assuming these points to win%s represent the value of points, the following may be assumed(?):
Given 2 equal teams, giving either team 2 points would increase their win probability from 50% to 52.65%.
Given a team with a 52.65% win probability, our best estimate as to margin of victory is 2 points.
Who knows how accurate these point margin of victory to win%s will be in the future, but is was based on quite a lot of actual results data.
Feel free to tear this analysis apart, I'm only human and may have missed something.