## Chance of a Football Team Winning Knowing the Vegas Spread

Update - I have added curves using binary logistic regression fit as Joelestra describes in the comments.  Thanks to Joelestra for the curves.

I know that this website specializes in baseball topics, but this year I plan on doing a few number based football articles.  I hope I don't throw everyone, especially Sky, into too much of a frenzy.

With football around the corner and only trophy the Royals are contending for is Bryce Harper, which they will screw up, I will turn to a little football. Vegas is always looking at how much a team wins by, but as a football fan I always wanted to know the chances of a team winning knowing the spread. I was able to find the NFL spreads and results from 2004 to 2008 and college spreads and results from 2005 to 2008. I calculated the separate win loss records for for college and NFL.

Note: The college games from 2005 don't have ½ point lines.

I weighted the winning percentage chance of winning at each value to 50% for that specific line, 16% for each ½ point away and 9% for each 1 point away. this adjustment helped even the impact a huge upset, such as Stanford's 24-23 upset of USC when they were a 39.5 point underdog.   Also more spreads are at even numbers, vice ½ increments, so this help to smooth the winning percentages from one value to the next.

I have created a chart of where the winning % chance breaks are for various spreads and a graph that plots out the weighted values versus chance of winning. There is an equation on each graph for estimating the chance of winning knowing the spread for easy calculations.

#### NFL - % Chance of Winning vs. Spread

 % Chance to Win Spread 100 -15 90 -95 -14 85 -11.5 75-80 -8 70 -7 65 -5.5 60 -3.5 55 -1

#### College - % Chance of Winning vs Spread

 Chance to Win Spread 100 41 95 21.5 90 16.5 85 16 80 14 75 13 70 6.5 65 5.5 60 5 55 2

So now you know when your college alma mater is a 14 point under dog, the team has about a 20% chance to win and knowing is half the battle.

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