Compiling Match Odds (Part I) - UPDATE

Nice to see my last post generating some interest, and it’s always good to receive comments whether they be good or bad. I’ll answer the comments I did receive now

Dave from Betfair Football Trading  said this:
Nice post Eddie - I've been looking for something like this for a while and am looking forward to the other methods hinted at. But... I'll be damned if I can see the home calculation - I'm getting 46.54 indicating odds of 2.15....

Initially I just assumed that in my rush to get the post out, I'd made a basic mistake (not unknown for me). However, on looking at it, I realise that my original post was not as clear as it could have been. I mentioned average home/away win percentages and then used those in calculations. What I should have done is to convert those for the reader. So 46.47% should be 0.4647 in the given calculations. Apologies for any confusion, and as I say I have now changed the original post to make it clearer.

I also had a comment left by Cassini from Green All Over:
Surely your goal differential numbers need to account for the strength of the opposition? Last six games versus Wolves, Bolton, QPR etc. is a lot different to playing the Manchesters, Arsenal, Chelsea etc.

Cassini is of course absolutely right – if we’re trying to manipulate our match odds into being as accurate as humanly possible, then it only makes sense to factor in the quality of opposition that our teams have previously faced. However, before we go rushing off and start changing the Goal Supremacy algorithm, there are a couple of things to consider.

First off, I purposely didn't include any additional weightings for this when constructing the Goal Supremacy match odds for Arsenal v Spurs. Initially I just wanted to show just the raw Goal Supremacy calculation. The way I have shown it is without any extra weighting for strength of opposition, which is its unadulterated form. It can always be built upon later.

This leads me onto the second point. Adding-in further weightings for the strength of opposition is jumping the gun. We've only just started exploring this area and we don't want to get ahead of ourselves. Cassini is obviously experienced and, by the sounds of it, has worked hard to acquire a mature set of algorithms for his ratings. Not everyone is in such a position.

Furthermore, the post on Goal Supremacy is one in (hopefully) a series of posts on the subject of compiling match odds - and the other areas I intend to cover, such as Rate Form, are more suited to determining the strength of opposition.

As such, this leaves us with a choice to make: should we insert additional weighting for each and every ratings method that we use? Or should we allow the other rating methods that we will be exploring to themselves act as the additional weights in an overall calculation of match odds? You’ll have to decide for yourselves which method you prefer, but personally, I don’t add weighting to each and every method – I allow each method to counterbalance the other, which then allows an overall determination to be formed.

An argument in Cassini’s favour here is that if we backfit each method as a standalone calculation, using weights to determine a “best-fit” for past results, then each method should eventually be stronger in its own right. Then in combination we could have an even more powerful and accurate prediction method for determining the odds.

Then again you may say that if some of these ratings methods are specific in their dealings with opposition strength (and some are), then trying to also shape those ratings that don't naturally lend themselves to that aspect could warp or skew an overall calculation. Perhaps we should allow each rating to do what it's best at?

Each of these argument has its own merits, I suppose; and you’ll have to decide for yourselves which camp you belong to. You should be aware, however, whichever one you choose, you will still be raising yourself above the massed throng of bettors out there who make their selections on little more than gut feeling or hope.

The final comment that I want to show is this one from Cloppa:
Great post. So you just look at the last 6 games regardless of competition? Should you be looking at league games only if you’re focusing on a league match.

Cloppa is absolutely right. Cup competitions should be looked at in isolation, and I don’t generally take notice of them when calculating Goal Supremacy for league matches. My post did include cup competition scores so this was a mistake. You, however, may decide otherwise.