2011-2012 predictions

2011-2012 predictions start when teams have played two home games and two away games each. So a few weeks away yet.

Scibet

I hadn't previously noticed that http://www.scibet.com has an archive of their predictions for previous seasons. At least I think that's what the "Results" pages are. They're not labelled very well. Anyway, I investigated a bit, and found that my own method makes more money, except in the last quarter of the season, where Scibet's average and variance are both higher. Maybe English leagues are a weakness for them.

Kelly shortcomings

The Kelly bet isn't perfectly suited to football betting. It gives the optimum stake size when making repeated bets at the same odds and probability, but this is not the situation in football betting. And it can't help when placing bets on several markets at the same time either.

Kelly bug

There was a bug in my Kelly calculations! Effectively I was using the estimated probability as the stake size instead of the proper Kelly calculation. Hopefully when I retest with the correct calculation the results should be better.

Unfortunately I think this is a symptom of being forced to work on my system in very short bursts and thus lacking time to refactor and fix bugs. I wonder how many bugs remain...

Divide and conquer

I've been experimenting with splitting up the season into sections and treating them separately, with some success. The first half of each season seems pretty intractable though.

Resetting every season

I think resetting the model every season was perhaps a mistake. It makes it too sensitive to periods of unusual results. Now that I have data from several seasons, it's more feasible to experiment with using the last few seasons for prediction.

But I still think using too many past seasons should be avoided. My feeling is that the game changes pretty quickly, so the factors which will predict results will also change pretty quickly.

Past seasons

After tweaking my model for the 2009-2010 and 2010-2011 seasons, I tried it out on previous seasons. It showed mixed results:

2003-2004 reasonable profits
2004-2005 good profits
2005-2006 big losses
2006-2007 reasonable profits
2007-2008 small losses
2008-2009 good profits
2009-2010 huge profits
2010-2011 big profits

I need to decide how much these results matter to me. Of course I would have been happier if every season had showed a profit, but the 2005-2006 season was five years ago, which is a long time.