The Church of Betting

Rating Models: Goal Ratings

Rating Models: Goal Ratings

If you have read my article on Profitable Sports Betting strategies, you already know that you can make a lot of money by finding an edge in the betting markets and that finding an edge in the betting markets is very hard. How does one go about it? There are several ways to approach this problem but, but a popular one are Rating Models and Goal Rating Models in particular. Rating Models are a favorite topic of mine and I have written a very detailed article on the steps of building a Rating Model. I strongly recommend to give it a look if you want to excersise model building in practice.

What actually inspired me to dive into Rating Models was the football-data.co.uk website of Joseph Buchdahl. Joseph has written a great article on that matter: Rating Models. I also strongly encourage you to give his book “Fixed Odds Sports Betting” a try – rating model basics are discussed in more length there, next to staking plans and risk management. Definitely an interesting read.

The Basics of Rating Models

The concept of Rating Models is to calculate the probability of a certain team winning a game against another based on the two teams’ relative strength (also called Rating). The trick here is to find a good way to measure this strength that incorporates both the fundamental value of the teams and their recent form, as well as assessing correctly what influence the two factors have upon a team’s results. Let us have a look at an example – a Goal Rating Model based on goals scored in Association Football

A practical example

Goal Rating Models - Starting Steps

In the article quoted above you can see that a simple goal form model appears to find an edge in the British football betting market. I have replicated the model using the goals scored for and against a team in its last 6 games, but this time I made the calculations not only for England, but also for Scotland, Italy, Spain, Germany and France. The data used comes from football-data.co.uk. I have formed the equation from all seasons till 2014/15 and used season 2015/2016 to test the profitability of the strategy. The equation was calculated only for home teams, since we already know it has the highest explanatory power there. Here is what I found:

England:

 with model (best odds)
with model (average odds)
all home wins (best odds)
all home wins (average odds)
bets
1369
1159
2236
2236
profit-11.62
-74.92
-42.3
-159.96
yield

-0.85%

-6.46%
-1.89%
-7.15%
y = 0.0120944830x + 0.4533594773
R² = 0.9747701268

Scotland:

 with model (best odds)
with model (average odds)
all home wins (best odds)
all home wins (average odds)
bets
328
282
640
640
profit75.48
36.98
41.99
-12.43
yield

23.01%

13.11%
6.56%
-1.94%
y = 0.0150124252x + 0.4321361372
R² = 0.9614325276

Spain:

 with model (best odds)
with model (average odds)
all home wins (best odds)
all home wins (average odds)
bets419353656656
profit-3.41
-26.4
9.48
-23.59
yield

-0.81%

-7.48%
1.45%
-3.60%
y = 0.0114462462x + 0.4780770646
R² = 0.9271078320

Germany:

 with model (best odds)
with model (average odds)
all home wins (best odds)
all home wins (average odds)
bets326286
504504
profit-12.9
-35.24
-5.08
-32.22
yield

-3.96%

-12.32%
-1.01%
-6.39%
y = 0.0110592808x + 0.4709960837
R² = 0.9276883121

France:

 with model (best odds)
with model (average odds)
all home wins (best odds)
all home wins (average odds)
bets436370
640640
profit-42.9
-79.47
-31.52
-63.02
yield

-9.84%

-21.48%
-4.93%
-9.85%
y = 0.0116382314x + 0.4807301722
R² = 0.9412016660

Similarly to the original study I have found the strategy to return a premium in England, although it is still not profitable mainly due to poor performance of the home teams. In Scotland the strategy was profitable and had an edge in front of a blind home-backing strategy. However, in the other tested countries the strategy failed to deliver.

How good are Goal Rating Models?

Although the results are not as promising as one would hope for we must not discard the strategy as useless. The differing results in different countries might just indicate a different style of play. Moreover, in England we have a much higher number of games to work with, which can give us more confidence in the results compared to other leagues.

Room for improvement

But mostly, we must keep into account that this is a very simplified system so it would probably be unwise to rely on it to deliver superior returns. There are a few obvious issues with it – it does not take into account against what teams the goals were scored and conceded. Another issue is that it does not differentiate between scoring and conceding home and away. Furthermore, the rating system does not weigh results based on how soon they occurred but just takes the average from the last 6 games.

In general, if one wants to build profitable Goal Rating Models, a lot more work must be invested to get rid of those imperfections and refine the calculation as much as possible. The stats and sources above are only meant to give you a starting point if you intend to go this route.

Alternatives

There are more refined rating systems, which take all those factors into account, most famously the ELO-Ratings. Needless to say, it is also more technically challenging to generate such ratings. However, one could also expect that their predictive power would be higher. There are even more complex goal rating models out there. I talk about in my article on Ratings, which account for a few of the issues with ELO. It pays off to familiarize yourself with the theory behind the different types of ratings before starting with model building.

I will continue with some historical odds analysis for my next article. There I will look into Goal Stats. This should be interesting for anyone who wants to build a Goal Rating Model. If you want to get updated on this and other new content, follow my Facebook and Twitter. Also, if you prefer some topics to be covered more extensively, let me know in the comments. See you around!

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