Football odds Generation

In the last blog we used the Poisson Distribution to predict the outcome for Man Utd vs Swansea.  How accurate was our prediction?  Let's compare with the book maker odds for the match.

When a bookie offers 9/1 they really mean 9 unfavourable outcomes to 1 favourable outcome - so that is 1 in 10 chance or a 10% chance of a favourable outcome.  We can translate all the bookies odds to an Implied Probability this way and compare with the probabilities that we generated.  Be careful here to realise that the bookies implied probabilities will add up to over 100%, this is where they make their margin.  For Paddy Power for the premier league matches that we are looking at, the probabilities add up to 108%.

I have applied my calculations to all the first round matches that I have enough data on.  The table below compares my calculated odds vs paddy power's published odds.

You can see that there is a large discrepancy in some case, eg about 4/1 vs 7/1 for Swansea against Man Utd.  But I do think that the bookies would quite happily offer some of my other odds.  For example the odds for Liverpool to draw, Man Utd to draw, Hull to win, Newcastle to draw, Stoke to win.

Obviously the bookmaker takes more into consideration than simply the teams past records - for example new manager, new players, injuries, even the weather.

Also I quite arbitrarily based my predictions on the last 3 seasons.  This could be tuned to more games (to get a more accurate long term average) or less games (to include more relevant data).  The optimum number of games to consider is not obvious but we could work our estimates better by trial and error.

Finally I discarded alot of information in creating my estimates.  So for example the Man Utd prediction I never considered Man Utd's away games.  This would have skewed my prediction (average away goals is not a good predictor of home goals), but they could be included provided some realistic weighting is given to them.

Match Outcomes			FoG		Paddy Power
Home	Away	Outcome	Odds	Probability	Odds	Implied Probability
Arsenal FC	Crystal Palace FC	Arsenal FC	5/7	0.5836	2/7	0.7778
Arsenal FC	Crystal Palace FC	Draw	13/4	0.2356	4/1	0.2000
Arsenal FC	Crystal Palace FC	Crystal Palace FC	9/2	0.1805	9/1	0.1000
Liverpool FC	Southampton FC	Liverpool FC	17/20	0.5399	4/11	0.7333
Liverpool FC	Southampton FC	Draw	13/4	0.2364	7/2	0.2222
Liverpool FC	Southampton FC	Southampton FC	7/2	0.2232	7/1	0.1250
Manchester United FC	Swansea City AFC	Manchester United FC	3/4	0.5697	4/11	0.7333
Manchester United FC	Swansea City AFC	Draw	17/5	0.2250	7/2	0.2222
Manchester United FC	Swansea City AFC	Swansea City AFC	39/10	0.2038	7/1	0.1250
Newcastle United FC	Manchester City FC	Manchester City FC	6/5	0.4585	8/13	0.6190
Newcastle United FC	Manchester City FC	Draw	3/1	0.2504	14/5	0.2632
Newcastle United FC	Manchester City FC	Newcastle United FC	12/5	0.2912	4/1	0.2000
Queens Park Rangers FC	Hull City FC	Queens Park Rangers FC	3/2	0.4030	13/10	0.4348
Queens Park Rangers FC	Hull City FC	Hull City FC	21/10	0.3279	2/1	0.3333
Queens Park Rangers FC	Hull City FC	Draw	27/10	0.2690	9/4	0.3077
Stoke City FC	Aston Villa FC	Stoke City FC	21/20	0.4885	11/10	0.4762
Stoke City FC	Aston Villa FC	Draw	29/10	0.2570	23/10	0.3030
Stoke City FC	Aston Villa FC	Aston Villa FC	29/10	0.2549	23/10	0.3030
West Bromwich Albion FC	Sunderland AFC	West Bromwich Albion FC	6/5	0.4538	13/10	0.4348
West Bromwich Albion FC	Sunderland AFC	Sunderland AFC	12/5	0.2930	2/1	0.3333
West Bromwich Albion FC	Sunderland AFC	Draw	29/10	0.2537	9/4	0.3077
West Ham United FC	Tottenham Hotspur FC	Tottenham Hotspur FC	7/4	0.3613	6/5	0.4545
West Ham United FC	Tottenham Hotspur FC	West Ham United FC	31/20	0.3907	21/10	0.3226
West Ham United FC	Tottenham Hotspur FC	Draw	3/1	0.2482	23/10	0.3030