Saturday, December 29, 2012

Bowl Game Line Predictions

The power rankings I create for this site are calibrated to a single purpose: to predict, as closely as possible, point spreads for future matchups.  I am trying to understand what (and how) the betting market thinks.  If my rankings worked perfectly, you would take the difference of the opposing teams' GPF (Generic Points Favored), add a home field adjustment, and the resulting number would equal the point spread.

Of course, my rankings do not work perfectly, and the predicted point spreads based on my rankings tend to miss, on average, by about 2.5 points (for college football). In a previous post, I compared my ranking's accuracy to the rankings provided by the Sporting News Linemakers section (the only other publicly available rankings system I'm aware of that has the same purpose as mine).  For the week I chose, I found that the predictive accuracy of the two ranking systems was about the same (my rankings had a mean prediction error of 2.1 points, compared to Linemakers' error of 2.2 points).

Thursday, December 27, 2012

Expected Points and Relative Team Strength

This is a continuation of a series of posts on in-game cover probability.  The purpose of this post is to show how relative team strength (as reflected in the point spread) can be factored into the concept of Expected Points.

In my kickoff post on the topic, I laid out two enhancements to the Advanced NFL Stats Win Probability Model that would be needed in order to develop a proper cover probability model:

1. Probability estimates that factor in the a priori relative team strength implied by the point spread.
2. Estimates of scoring margin distribution, not just a binary win/loss probability

I have not made much progress on either front at this point, largely due to the difficulties in just recreating Brian Burke's original work on Win Probability.  The problem is the sparseness of the data.  There just aren't enough actual game situations that feature, for example, a team down by 4, with 3rd and 2 at their 36 yard line and 2:30 to go in the 3rd quarter.  So, some careful interpolation is needed. Adding in the point spread as an additional independent variable only makes the data that much sparser and requires even more care when interpolating.  Adding margin distributions on top of that gives me LOST-style nosebleeds if I think about it too much.

Turnover Index - Final 2012 Results

Here are the final results for the Turnover Index for the 2012 season.  In my original post on the topic, I excluded week 17 games from the analysis, so there are no more betting opportunities this season.

Week 16 Results

Things ended on a low note, with the week 16 picks going 1-3 against the spread.

Turnover Index through Week 16 (Against the Spread): 18-16-1

That's 52.9% against the spread.  Assuming the standard sportsbook bet (lay $110 for a chance at a $100 profit), you would have realized a whopping 1% return on investment.  That's below the long term performance of 59% against the spread observed from seasons 1998-2011, but at least it's positive.

So what, if anything, went wrong?

Wednesday, December 19, 2012

Turnover Index - Week 16

Here are the Turnover Index numbers for Week 16 of the NFL season.  The purpose of these weekly posts is to find betting opportunities that exploit the market's tendency to overvalue a team's season to date defensive turnovers.  See here and here for more background.

Wednesday, December 12, 2012

Turnover Index - Week 15

Here are the Turnover Index numbers for Week 15 of the NFL season.  The purpose of these weekly posts is to find betting opportunities that exploit the market's tendency to overvalue a team's season to date defensive turnovers.  See here and here for more background.

Wednesday, December 5, 2012

Turnover Index - Week 14

Here are the Turnover Index numbers for Week 14 of the NFL season.  The purpose of these weekly posts is to find betting opportunities that exploit the market's tendency to overvalue a team's season to date defensive turnovers.  See here and here for more background.

Sunday, December 2, 2012

Alabama - Notre Dame Opening Line

In this post, I made a prediction on the point spread and over/under for the two possible BCS title games (Notre Dame vs. Alabama or Georgia).  Even though the game has not been officially announced, Vegas is not wasting anytime (this game is projected to be the most heavily bet game ever).  Opening lines are available and it looks like my prediction favored Alabama too much (by about 3 points).

My rankings as of November 25 predicted Alabama as an 11 point favorite over Notre Dame.  Even prior to the release of the line, that looked to be on the high end of estimates I could find from gambling experts, where things ranged from 7 points to 11 points.  In an earlier post this week, I put my rankings to the test against the Linemakers' rankings.  According to their November 28 rankings, Alabama should have been a six point favorite.

Things still seem to be a bit fluid, but best as I can tell the line is currently 8 points in favor of Alabama, which means my prediction was off by 3 points.  However, my rankings are calibrated to closing lines, so I will probably check in at least once prior to the title game to see which way the line moves.

Saturday, December 1, 2012

Today's Games now available for the NBA

Now that the NBA rankings are up and running, I can now relaunch the Today's Games feature of this site.  Here is a description of what this feature is intended to do (you can also see here for additional background).

Today's Games

The main purpose of this feature is to highlight "unexpected" point spreads and over/unders for games to be played that day.  I can calculate expected point spreads and over/unders using my betting market rankings (see the Methodology page for a description of how the rankings are derived, and see the end of this post for how to use the rankings).