Saturday, 28 April 2012

Injury Crisis

The XX Draw Selections had one winner from one selection today as Stoke City and Arsenal drew 1-1 at 3.8, and win for the Unders also at a generous 1.98. Peter Nordsted also picked this as one of his Drawmaster selections, and he also found West Bromwich Albion v Aston Villa (0-0) for a profitable day.

Pete's third draw pick was the Wigan Athletic v Newcastle United game, and as I wrote earlier today, this for me was a value Wigan back, and the game finished a comfortable 4-0 to Wigan.

Football Elite went for Norwich City v Liverpool (Draw No Bet) but, again as I wrote earlier, for me this was a big value back of Liverpool.

Geoff came up with his usual Saturday selection of eight draws, and found two for a small loss on the day. This week saw Geoff finding selections in the footballing hotbeds of Lillestrom, Stabeek, Sogndal and Annan.

BigAl suggests that my post stating that "There has been an increase in goals this season, which clearly affects the probability of a game resulting in a draw." is somehow meant to imply that it applies to the probability of games yet to take place. My words could well have been better chosen, but I think that 99.9% of readers understood what I meant, especially given the context of the post, i.e. the 2009-10 season, and the unusual results up to that time. BigAl seems to be stuck on his idea from the world of Blackjack that probabilities in football are dependent.

What BigAl finds so hard to understand about more goals meaning less probable the draw, I'm not sure. A look at the low scoring Ligue 1 in France and the high scoring Bundesliga might make it clearer.

In the Bundesliga since 1998-99 there have been six seasons where the average goals per game has been 2.9 or higher and in those seasons the percentage of draws was 23%, 22%, 24%, 21%, 24% and 21%.

Contrast this with Ligue 1 where six seasons in this period saw an average goals per game of 2.28 or lower. In those six seasons, the draw percentages were 28%, 35%, 31%, 31%, 31% and 29%.

There is a reason why the draw percentages are so consistently different.

BigAl also came up with his much anticipated explanation of how an increase in goal expectancy makes a draw more likely. He writes:
Imagine a team with a strong supremacy (x) in a match with goal expectancy (y)
That team then loses its entire defence to injury just before the match.
(x) and (y) obviously change.
Is it possible for this change to result in higher goal expectancy but a more probable draw?
Yes it is. Not probable, but possible.
One significant detail missing is that the opposition's goal expectancy (z?) increases in this scenario, and the goal expectancy (y) for our unfortunate team would be only slightly reduced - if at all.

Anyway, there you have it - look for matches where the stronger team loses "its entire defence to injury just before the match", (it happens all the time), back the overs, and back the draw.

Not probable, but possible. Indeed - and for those of us living in the real world, and dealing with probabilities rather than possibilities, I respectfully suggest we continue looking at the numbers, and understanding that the probability of a draw is the sum of the Correct Score probabilities of 0-0, 1-1, 2-2 etc. and that most draws are either 0-0 or 1-1 (unless of course your name is Geoff, in which case you find 3-3s all the time!)

Backing Ian Erskine's Lay the Draw selections lost a couple of points today with Schalke '04 winning 4-0 and Gijon winning 3-0.

The XX Extended (Bundesliga) Draw selections had one winner from two today with Hamburg and Mainz '05 playing out a perfect draw, although the less said about the second qualifier, the better. When a game has five goals in it, I hope we can all agree, the probability of the result being a draw is slim. Cue for BigAl to comment "Imagine a world where penalties count as 0.5 goal, and both teams score a penalty.... not probable, but possible".

Sogndal are still in-play, and more matches tomorrow before I'll publish the latest Friendly Tipster League standings.


BigAl said...

Another nice job of showing your ignorance of certain intricacies of match pricing. Well done.

Yes, of course the opposition's goal expectancy increases. That's the whole point of the example!

Now, as I understand it, your somewhat simple system of backing draws essentially identifies matches where the supremacy is low. Genius.

Anyway, if expected goals were to increase, let's say because of just one injury to a very important defender for the favourites, their supremacy will decrease.

Furthermore, depending on the initial expected supremacy it's surely possible for the supremacy to decrease to within your defined limits and therefore trigger a bet on the draw.

In which case your system would now be backing the draw in a match where expected goals have risen. Yet, with lower goals, before the injury news, you wouldn't have backed the draw.

Of course there's a major flaw in the above theory: You of course don't adjust your numbers for team news - probably the most common mistake made by amateur bettors. Indeed you wouldn't know where to start.

But even so, perhaps the above will help you realise the inadequacies of your methods and beliefs. Sadly, somehow I doubt it.

BigAl said...

"the probability of a draw is the sum of the Correct Score probabilities of 0-0, 1-1, 2-2 etc"

Correct of course - for a change.

But the truth is that you personally don't (can't) even calculate these correct score probabilities before backing your draws. You simply back the draw - at whatever price happens to be available - when your ratings tell you to.

I look forward to you claiming otherwise.

(the truth is you don't know how to accurately price the probability of a draw in an individual match. The evidence is in a post from some time back)