Tuesday 21 February 2017

Verification and Validation

Although I'm sure there was no intent by Brian to mislead anyone, I did clarify in my last post that the average number of goals per match in the Premier League is not 2.4 as asserted, but closer to 2.75. For this season, it's actually at an all-time high of 2.82. 

As this actual total moves from below the 2.5 level to above, it's not surprising that some of Brian's conclusions are wrong. 

As anyone studying the Over / Under markets in the Premier League will also be aware, since 2015-16 (630 matches at the time of writing), blindly backing the Overs has an ROI of over 5%.  

Over this time, 46.7% of matches went Under 2.5, while 53.3% go Over.   

A couple of filters improve this ROI still further. One I'll give away is that where the implied probability for the Overs is in the 40% to 50% range, the ROI is closer to 8.5% from 314 matches.

The alternative filter eliminates about two-thirds of matches and has an ROI of 15.9% from 212 matches. 

I just noticed that Brian has emailed me regarding my post, saying:
I'm really pleased your enjoying my blog. I have quite a few topics on my list that I hope to write about and your feedback as well as your own writing is always inspiring. You're right about that sentence and I still have to curb my tendency to rush my thoughts down at times!
The 2.4 goals stat for the PL I got from a Pinnacle article written last year but if it's incorrect that'll teach me not to do my own calculations. I am surprised it's as high as you've found though.
However you calculate the average goals per game for the Premier League, it's never been as low as 2.4 unless my numbers are wrong. The low for a full season was 2.45 in 2006-07, but perhaps I should have kept quiet as all those squares assuming the average was around 2.4 will now be driving the Overs price down. 

I'd not read the Pinnacle article before, but it's not one of their finest. The writer, Dafni Serdari, says this:
To give you a better idea about differences in the average goals per game across the major European leagues, Premier League matches have an average of 2.4, Italy’s Serie A whopping 3.21 and Spain’s La Liga 2.85 goals per game.
Nonsense. Serie A has 'whopping' 3.21 goals per game? I don't think so! I make it exactly 2.6 goals per game over the last ten full seasons, and the highest it has been this millennium is 2.76!

In La Liga, I have 2.73 goals per game in the last ten seasons which is close, but when you're looking at numbers in this way, you need the data to be correct. 

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