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Probality Theory/Formula
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Could you please explain this to me in laymans terms please.i.ie. for chelsea to beat arsenal.and show me how to apply it
thanks
thanks
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http://www.peterwebb.co.uk/probability.htm
is a pretty good layman's guide to probability theory.
He puts in something about forecasting correct scores, but one obvious difficulty with his system is that it looks only at how many goals the two teams in the example score - obviously it should take into account the number of goals they concede as well. But you should beware of averaging out the figures.
Last season in the EPL, home teams scored an average of 1.46 goals per game, while away teams scored an average of 1.02.
So lets say that team A averages 2 goals scored per game at home, and team B concedes an average of 2 goals per game. Does that mean that team A can expect to score 2 goals against team B? No; team B is conceding more than the average number of goals in its away games, and team A is scoring more than the average in its home games; if the teams haven't changed, team A could expect, on average, to score 2.76 games in a game against team B (this is (team A's goals/average for the division)*(team Bs goals/ average for the division)* average for the division)
Use this method, however, too many, and you'll go back too far to a time when the teams were different - Chesea and Arsenal are different from what they were a few months ago because of Gallas and Cole changing clubs, not to mention all their other transfers.
Use too few games and you run the risk of having a freak result - particularly one high scoring game - skew your figures.
Nonetheless, if you are happy with using goalscoring expectations to forecast your results, this is what you should do - if you have Microsoft Excel.
continued . . .
is a pretty good layman's guide to probability theory.
He puts in something about forecasting correct scores, but one obvious difficulty with his system is that it looks only at how many goals the two teams in the example score - obviously it should take into account the number of goals they concede as well. But you should beware of averaging out the figures.
Last season in the EPL, home teams scored an average of 1.46 goals per game, while away teams scored an average of 1.02.
So lets say that team A averages 2 goals scored per game at home, and team B concedes an average of 2 goals per game. Does that mean that team A can expect to score 2 goals against team B? No; team B is conceding more than the average number of goals in its away games, and team A is scoring more than the average in its home games; if the teams haven't changed, team A could expect, on average, to score 2.76 games in a game against team B (this is (team A's goals/average for the division)*(team Bs goals/ average for the division)* average for the division)
Use this method, however, too many, and you'll go back too far to a time when the teams were different - Chesea and Arsenal are different from what they were a few months ago because of Gallas and Cole changing clubs, not to mention all their other transfers.
Use too few games and you run the risk of having a freak result - particularly one high scoring game - skew your figures.
Nonetheless, if you are happy with using goalscoring expectations to forecast your results, this is what you should do - if you have Microsoft Excel.
continued . . .
In cell b1, put 0
In cell c1, put 1
And carry on until you have as many goals as you think one team can score - probably 5
In cell b2, put this formula:
=POISSON(b1,$a$2,false)
Highlight cell b2, and use the copy/fill function to put the formula in all the columns in which you have put a number in the top row - if you went up to 5 goals, this will be columns c2, d2, e2, f2 and g2
In cell b3, put the formula
=POISSON(b1,$a$3,FALSE)
Copy and fill this formula to cells c3, d3, e3, f3 and g3
Highlight the block of cells in which you have put those formulas
Click format - percentage - 1 decimal place
Now in cell a2 put the number of goals you expect the home team to score, on average
And in cell a3 put the number of goals you expect the away team to score on average
Cell b2 will show the %age chance that the home team will score 0 goals, if your estimate were correct
Cell b3 will show the %age chance that the away team will score 0 goals
Cells C2 and c3 will show the chance of the teams scoring exactly 1 goal
Cells D2 and D3 will show their chances of scoring exactly 2 goals
and so on.
Then you can cross-multiply to find chances of a home win, draw or away win.
However . . . .
This sytem takes into account only the two teams' past records.
It doesn't look at current form.
It doesn't take into account injuries or suspensions.
It doesn't take into account the head-to-head records of the two teams.
It doesn't take into account who the referee is going to be.
And it doesn't take into account all the myriad things that can affect a game of football - and it wouldn't have taken any of those things into account for any of the games
In cell c1, put 1
And carry on until you have as many goals as you think one team can score - probably 5
In cell b2, put this formula:
=POISSON(b1,$a$2,false)
Highlight cell b2, and use the copy/fill function to put the formula in all the columns in which you have put a number in the top row - if you went up to 5 goals, this will be columns c2, d2, e2, f2 and g2
In cell b3, put the formula
=POISSON(b1,$a$3,FALSE)
Copy and fill this formula to cells c3, d3, e3, f3 and g3
Highlight the block of cells in which you have put those formulas
Click format - percentage - 1 decimal place
Now in cell a2 put the number of goals you expect the home team to score, on average
And in cell a3 put the number of goals you expect the away team to score on average
Cell b2 will show the %age chance that the home team will score 0 goals, if your estimate were correct
Cell b3 will show the %age chance that the away team will score 0 goals
Cells C2 and c3 will show the chance of the teams scoring exactly 1 goal
Cells D2 and D3 will show their chances of scoring exactly 2 goals
and so on.
Then you can cross-multiply to find chances of a home win, draw or away win.
However . . . .
This sytem takes into account only the two teams' past records.
It doesn't look at current form.
It doesn't take into account injuries or suspensions.
It doesn't take into account the head-to-head records of the two teams.
It doesn't take into account who the referee is going to be.
And it doesn't take into account all the myriad things that can affect a game of football - and it wouldn't have taken any of those things into account for any of the games
It's pity that I cant print out this, at least . I have to hand copy.
Using Hammond egg's, if you cross multiply, you will only get the chances of one goal each, two goals each, and in fact you need to have a full 5 * 5 matrix....
cross multiply - do a column - 1,2,3, and next to it a column 4,5,6 (so you know when cross multiplyig has worked...) IN the third column highligh a column of three and inn the box at the top, type = , then highlight column one, type * then highlight column two , and then press ctrl shift enter
magically in column three you should see 4 in the first cell, then in the second cell and 18 in the third. TRhen go and do it for your poisson array
in excell help, it is under 'arrays,'
I wouldnt use this, lovejoy - I am using it in a lecture in biology as an illustration of Poisson, I do not bet-it is a fools game.
Using Hammond egg's, if you cross multiply, you will only get the chances of one goal each, two goals each, and in fact you need to have a full 5 * 5 matrix....
cross multiply - do a column - 1,2,3, and next to it a column 4,5,6 (so you know when cross multiplyig has worked...) IN the third column highligh a column of three and inn the box at the top, type = , then highlight column one, type * then highlight column two , and then press ctrl shift enter
magically in column three you should see 4 in the first cell, then in the second cell and 18 in the third. TRhen go and do it for your poisson array
in excell help, it is under 'arrays,'
I wouldnt use this, lovejoy - I am using it in a lecture in biology as an illustration of Poisson, I do not bet-it is a fools game.
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