This is topic Betting probability of a win???? in forum Math-a-holics and Code Junkies at The Geek Culture Forums.

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Posted by Mikebyrne (Member # 5105) on August 14, 2009, 09:01:
When I look at the odds for a football match they are presented as (for example):

Liverpool: 5/6

Draw: 5/2

Spurs: 10/3

How could I work out the % chances of a win based on the odds??

ie Liverpool 70%
Draw 20%
Spurs 10%
Posted by TheMoMan (Member # 1659) on August 14, 2009, 09:12:
_____________________Mikebyrne ________________

Liverpool: 5/6 5/6= .83666%

Draw: 5/2 5/2= 250%

Spurs: 10/3 10/3= 333%

____ However this is the betting odds, and sometimes the players don't read the betting papers. They just go out and play their game, and the results are paid by the bookies.
Posted by Mikebyrne (Member # 5105) on August 14, 2009, 09:27:

I understand that 5/6 represnts a payout of 0.83 etc but I was jst wondering how I could compare all three odds and turn them into percentages ie 70% - 15% -15%
Posted by Stereo (Member # 748) on August 14, 2009, 09:51:
I'd go for lower common denominator. First reverse the odds, since the more chance of an outcome, the lower the payout, then get them on equat "footing":

Liverpool: 6/5 -> 12/10
Draw: 2/5 -> 4/10
Spurs: 3/10
Total: 19/10

Of course the total is greater than one, but that's the reverse payout. Now, you take each occurence on the total. (Results rounded to the unit.)

Liverpool: 12/19 -> 63%
Draw: 4/19 -> 21%
Spurs: 3/19 -> 16%

Again, that's how *I* think it's best done, but I could be wrong. I haven't touched that for years.
Posted by The Famous Druid (Member # 1769) on August 14, 2009, 16:30:
Originally posted by Mikebyrne:
How could I work out the % chances of a win based on the odds??

You can't.

The odds quoted are the prices bookies offer, in their effort to maximize their own profit. It's a balancing act between offering 'good odds' (to entice mugs to bet) and 'bad odds' (to reduce their payout after the game). The probability of the team winning is a relatively minor factor in the bookies calculations, it's more about punter psychology.

For example, Long-shot bias is a fairly well-known phenomenon in the gambling biz. In plain English, long-shot bias says punters are idiots, they'd rather bet on the long-shot that pays 20:1 than the 'sure thing' at 5:4, even though the probability of the long-shot winning is way less than 5%.
Posted by Mikebyrne (Member # 5105) on August 14, 2009, 16:52:
I've been using the formula (1-N/(N+M)*100 to get my percentages based on the odds.


Team A at 2/7 = 78%

Draw 5/1 = 18%

Team B 18/1 = 5%
Posted by littlefish (Member # 966) on August 14, 2009, 23:33:
I hope you realise that this is not a realistic view of the world.

Firstly, the probability of the actual outcome must be higher than the odds or the bookie makes no money. Bookies make lots of money.

Secondly, there is no way of predicting the future. Bookmakers do not know what the odds are, they take a conservative punt at it, but they change their odds according to what people bet on. If too many people are betting on one outcome, the bookie will decide that he is being too generous and lessen the odds. Basically, the odds are set by the hive mind.
Posted by Mr. Geek 2U (Member # 28663) on August 16, 2009, 16:43:

You seem pretty good with those numbers.

I live in Michigan and I am wondering what are the odds that the Detroit Lions will win a game this year?

THATS Mr. Geek 2U!

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