## Math vs. Vegas

I thought it might be interesting to compare my efficiency model's predictions with the consensus predictions. Probably the best estimates of the "consensus" predictions are the Las Vegas betting lines. Although I'm am not interested in gambling, betting odds and point spreads are useful as benchmarks for evaluating the usefulness of all this number crunching.

In this post I'll compare my 2007 predictions with the current over/under lines for season win totals.

The first thing that stands out is that my predictions are more aggressive. That is, my model goes further out on a limb by predicting wins further from the average (8 wins) than do the consensus predictions. In the AFC my predictions range from 4 to 12 (2 teams at 12) wins, compared to 5 to 12 (1 team at 12) wins for Vegas. In the NFC my predictions range from 5 to 12 wins, compared to 6 to 10 wins for Vegas.

6 to 10 wins is amazingly narrow. But this is a natural result of unconfident models. The less confident the model, the tighter the spread around the average dependent variable. Accordingly, we'd expect to see increasingly large differences in the predicted wins towards the top and bottom of each conference--which is exactly what we see.

The teams that show a big difference between the model and the consensus are of more interest. Notice that MIA, DEN, and NE have differences of at least 2 wins. The model is saying MIA is underrated, and DEN and NE are overrated. It's easy to understand the difference in NE's predictions considering their free agent acquisitions this year.

The notable differences in the NFC lie in the West. The model says SS is probably going to reliquish the division crown back to STL this year.

Note: The over/under lines are often in .5 increments. In these cases I rounded to the win total that is costlier to bet on, and therefore considered more likely. For example, if the line for a team is 9.5 wins and to bet on the 'over' it takes \$120 to win \$100, and to bet on the 'under' it takes \$115 to win \$100, I rounded to 10 wins. When the over and under were equally costly I left the prediction at a .5 increment.

### 3 Responses to “Math vs. Vegas”

1. Enda Byrne says:

Hey there. Love the site. Just have a question to ask about your me vs Vegas article. Do your predictions take no account for roster changes? For instance, Vegas says KC will win 8 games, you say 9 and I think both of you are crazy. That's because KC plans on starting Brodie Croyle at QB who is essentially a rookie. If Trent Green were the QB, I think 8 or 9 wins would be a very accurate estimate for the Chiefs. If they play Croyle for 16 games, I reckon they'll win 4 to 5.

2. Brian Burke says:

The predicitions do not yet incorporate personnel changes, which I think are often given far too much weight. They are meant as an unbiased starting point, based on the best hard information we have--last year's performance.

I’ve recently tried to account for personnel changes, at least for veteran acquisitions. Rookies would be too hard to project. For example, I just did a study on NE’s big name acquisitions which you can find on the main page.

I’m currently working on Trent Greene’s impact in MIA, assuming he remains conscious all season.

3. Anonymous says:

It's not exactly "gambling" if you manage money correctly over a long enough sample size and have a significant enough edge to win plus beat the fees/"juice"