AFL

OK guys, this is the formula for AFL starts/odds. You can use this formula to calculate the expected start from the odds on the favourite. It was quite different from the NRL formula, which looked more like a distribution. The AFL formula is kind of a modified exponential, with quite a bit of fudging from the line makers. I suspect the line is moved to try and maximize bookie profits, as it would be more subjective in a high-scoring game like AFL over NRL.

It seems that in AFL the bookies are a LOT more liberal with the relationship between starts and odds than the NRL. For instance, odds of $1.66 can vary from a start of -9.5 to -13.5. There is about a 3 point either-side shift in the lower starts, and in some places a 6 point movement in the higher starts.


ODDS = a / [ 1 + b * e^(-c * START) ]

OR

START = -Ln[(a / ODDS - 1) / b] / c

Where
a = 0.95
b = -0.58
c = -0.033

So for example, if the odds were 1.46

START = -Ln[ (0.95 / 1.46 - 1) / -0.58] / -0.033
= -Ln[ (0.65 - 1) / -0.58 ] / -0.033
= -Ln[ -0.35 / -0.58 ] / -0.033
= -Ln[ 0.60 ] / -0.033
= 0.51 / -0.033
= 15.55

The expected start is 15.5 +/- 3



This will work from about 1.01 to 1.90.

You might find it easier to copy this to a Excel SpreadSheet.

Jake.