xG - What's it telling me?

Football, Soccer - whatever you call it. It is the beautiful game.
spreadbetting
Posts: 1055
Joined: Sun Jan 31, 2010 8:06 pm

Wed Jan 03, 2018 5:08 pm

MemphisFlash wrote:
Wed Jan 03, 2018 4:35 pm
i'll tell you what it is. it's a load of bollocks.
Past performance is no Guarantee of future expectancy!!!
Of course nothing's guaranteed but all probabilities are generally derived from past performances especially where you have related data. Saying it's a load of bollocks is like saying we should ignore all horse's form lines when setting odds.

The odds with football are so modelled it's hard to find an edge so every little helps if you can get it to work for you. I used to track actual results against the expected results to see if I could find any trace of teams that were outperforming or underperforming expectations.

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ShaunWhite
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Joined: Sat Sep 03, 2016 3:42 am

Wed Jan 03, 2018 5:19 pm

spreadbetting wrote:
Wed Jan 03, 2018 5:08 pm
MemphisFlash wrote:
Wed Jan 03, 2018 4:35 pm
i'll tell you what it is. it's a load of bollocks.
Past performance is no Guarantee of future expectancy!!!
Of course nothing's guaranteed but all probabilities are generally derived from past performances especially where you have related data. Saying it's a load of bollocks is like saying we should ignore all horse's form lines when setting odds.

The odds with football are so modelled it's hard to find an edge so every little helps if you can get it to work for you. I used to track actual results against the expected results to see if I could find any trace of teams that were outperforming or underperforming expectations.
"used to" ? Can I take it from that that you didn't find it helpful?.

I think it's reasonable to start from the assumption that everything is bollocks, until proven otherwise.

phrenetic
Posts: 17
Joined: Sun Oct 16, 2016 5:11 pm

Wed Jan 03, 2018 5:35 pm

There's an article on Pinnacle about xG at the moment - https://www.pinnacle.com/en/betting-art ... g-formula/

spreadbetting
Posts: 1055
Joined: Sun Jan 31, 2010 8:06 pm

Wed Jan 03, 2018 5:48 pm

Unfortunately it didn't give me any edge at the time possibly because i didn't put enough effort into it at the time because my coding skills were too limited for the data churning I was looking to do. The thing with football is there's so much data out there that backtesting systems based on snapshots in time aren't neccessarily too hard. I use football mainly for generating commission these days but I do see it as the holy grail because if you can get any small edge the money going through the markets will bring huge rewards.
ShaunWhite wrote:
Wed Jan 03, 2018 5:19 pm


I think it's reasonable to start from the assumption that everything is bollocks, until proven otherwise.
I actually approach all my betting ideas from the opposite angle, I start with something I think should work and the reasons why I think it'll work then test in the real world to see if my presumptions are correct or not. I think it's always best to approach systems etc with preset ideas as I find they're much easier to prove or disprove and disproving your ideas generally reveals the reason why you were wrong to make the assumption in the first place, if that makes sense? I think a lot of traders fail becuase they use a scattergun approach and it's so hard to deduce anything worthwhile if there's too many variables on the go.

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ShaunWhite
Posts: 1816
Joined: Sat Sep 03, 2016 3:42 am

Wed Jan 03, 2018 6:04 pm

phrenetic wrote:
Wed Jan 03, 2018 5:35 pm
There's an article on Pinnacle about xG at the moment - https://www.pinnacle.com/en/betting-art ... g-formula/
Didn't see anything very illuminating in that.
He'd created his own xG 'model', with no particular evidence that it was accurate.

"First, use logistic regression to find inconsistencies in the odds, then add in variables (such as expected goals) to see if you can get an edge. This edge will be small, but it could well pay off in the long term."

This is possibly the most vague conculsion I've seen for a while.
"Add in 'variables'" (including a homebrewed xG)
"see IF you can get an edge"
"COULD pay off in the long term"

..but the oddly says it "WILL be small"

All that maths and graphs didn't impress me a great deal.
I see on the other pages that they're another person who uses the word 'model' to describe a process to arrive at a betting system, when a 'model' is actually a precise description of entity relationships from which cause and effect can be established.

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ShaunWhite
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Joined: Sat Sep 03, 2016 3:42 am

Wed Jan 03, 2018 6:07 pm

spreadbetting wrote:
Wed Jan 03, 2018 5:48 pm
I actually approach all my betting ideas from the opposite angle
Different start, same end hopefully.
It doesn't mean I won't entertain new ideas, it's just that I find that I'm much more rigourous when proving I'm wrong, than when I'm proving I'm right.

phrenetic
Posts: 17
Joined: Sun Oct 16, 2016 5:11 pm

Wed Jan 03, 2018 6:22 pm

Aren't all xG calculations "home-brewed"?

DoctorEvil
Posts: 12
Joined: Wed Jun 21, 2017 9:07 am

Wed Jan 03, 2018 6:25 pm

ShaunWhite wrote:
Wed Jan 03, 2018 3:10 pm
Again, I've never seen xG figures for a match yet to be played, it's historical analysis isn't it? A twist on 'chances created'.
I never heard xG is used to count chances/dangerous situations in a game by adding all the probabilities of scoring a goal in each of those situations. to me that doesn't really make much sense since assigning a value to this probability is hard. i've seen a heat map of probability of scoring from some area, but it's just general. shot from 10 meters can be pretty safe for the defending team if it's a header after corner that doesn't have power or accuracy, or it can be an almost certain goal if it's a cutback to an unguarded player.

I thought xG can only be used in some kind of a regression model with outputs being expected goals scored.

spreadbetting
Posts: 1055
Joined: Sun Jan 31, 2010 8:06 pm

Wed Jan 03, 2018 6:28 pm

ShaunWhite wrote:
Wed Jan 03, 2018 6:07 pm
spreadbetting wrote:
Wed Jan 03, 2018 5:48 pm
I actually approach all my betting ideas from the opposite angle
Different start, same end hopefully.
It doesn't mean I won't entertain new ideas, it's just that I find that I'm much more rigourous when proving I'm wrong, than when I'm proving I'm right.
I always leave it to the markets to tell me if I'm right or wrong, that's a much better judge than me :D

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ShaunWhite
Posts: 1816
Joined: Sat Sep 03, 2016 3:42 am

Wed Jan 03, 2018 10:35 pm

spreadbetting wrote:
Wed Jan 03, 2018 6:28 pm
I always leave it to the markets to tell me if I'm right or wrong, that's a much better judge than me :D
I think I'll use that as a new year's resolution... It'll save me hundreds of hours of staring at excel only to be crushed in the real world :)

I'm not seeing many replies by people who are fans of xG. Opinion seems to range from Memphis to being luke warm about it.

I'm puzzled by why MoTD have started showing it. I suspect someone has a vested business interest in selling data, in the same way as the BBC always say iPhone when they mean smartphone and Twitter when they mean social media despite allegedly not being able to promote products.

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