Tuesday 29 April 2014

Defending The Draw

It was another 'below expectation' weekend for draws across the top five leagues in Europe with just 11 from the 49 matches, four of which were in the Bundesliga. This follows a round of 11 from 48 matches, and the 2013-14 strike rate for draws continues to be below long-term averages in all leagues:

Danny Murphy questioned (very politely) my assertion that the reduced number of draws in the leagues I track, relative to their long-term averages, is a valid excuse for a negative ROI on my draw selections.

He wrote:
Still trying to get my head round your comments about the lack of draws in the five leagues.
It's hard to explain but how can you be sure about the link between the lack of draws in the matches you have selected and the lack of draws in the league in general? I don't see why a lack of draws in the league would affect your selections. Once your selection has resolved itself the other results won't matter. If I back Man U to win at home and they draw what does it matter if home wins have been less in the PL this season? I don't see any relationship between one and the other. Yet I have to admit your excuse sounds highly plausible until you really start thinking about it.
In a way you are saying you aren't doing well because draws have a random element to them. But I say don't back the draw for exactly that reason, they are almost impossible to predict and it's going to be very difficult to find much of an edge.
My reply was:
I understand where you’re coming from, but the issue for me is that the predictive model (it really does sound pretentious when all it is a spreadsheet) is built on Elo ratings and data from previous seasons in the leagues I follow. The idea is that over time, 10 years plus, the numbers of Home wins, Away wins and Draws, as well as goals scores tend to be remarkably consistent within each league.

Each national league has its own ‘personality’ and this is factored into the model. So the model makes a broad assumption that in say the EPL, the Home wins will (over time) continue to be around 47% of matches, with the Aways around the 27% mark and the Draws 26%.

(There’s a reason why there are usually around 14 draws each week in the XX Draws selections).

Over a season, this assumption would usually be reasonable, but in an extended period such as this season, the template for the model simply isn’t a good fit, not just in one league but in four of the five. The model would slowly adapt, but more likely is that the reduced percentage of draws is not a long-term trend, just one of those outliers that come along every once in a while. It’s just very unusual to see the same trend across all the leagues in the same season.
I went on a bit more about specific numbers, (it made me feel better but probably bored Danny to tears - he's not written to me since), but if we take an extreme example, if this season had been one where the draw percentage was say 33%, i.e. considerably higher than the model 'expects', it is almost certain the XX Draws would have looked great, and almost as certain that I wouldn't have paid so much attention as to why.

As for Danny's last comment, I agree to a point. Draws are often random, but if the selections are games where the 'true' goal expectancies are lower than the market's expectation, the draw will be value. The 0:0 is the perfect draw, the 1:1 isn't too shabby, but I don't get too upset about the 1:0 or 0:1 results. The randomness that makes football such an exciting game means that while you can't predict exactly which matches will result in draws, you can predict the matches where it is more likely that the prices suggest.

Certainly 3:3 (or higher scoring draws) are fluky and the 2:2 result doesn't exactly fill my heart with joy, but the 0:0s and 1:1s are pleasing enough.

Given the efficiency of the match odds markets, any edge is always likely to be small, but the pool is a reasonable size for a part-time investor - 1,826 in the big five, but many more if you care to include the lower leagues or some of the other leading leagues.

The big question for me is whether the lack of draws this season is an anomaly or the start of a trend. More goals means fewer draws as I have written before, and it is a fact that there are more goals being scored this season in all five top leagues than their 10 year averages. What is not clear to me is why this is so.

No comments: