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Old 01-24-2013, 09:16 AM   #41
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Location: NorCal Bay Area
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Originally Posted by jmnk View Post
Well, we just have to disagree here.
Actually, no, you have convinced me, so I recant
Originally Posted by jmnk View Post
In practice, for USTA tennis you can easily normalize via the following:
'the best possible result' is 12 games difference (6:0, 6:0 score) - so that is '1' in ELO calculations
'the worst possible result' is -12 games difference (0:6, 0:6 score) - so that is '0' for ELO calculations.
'the tie' is 0 game difference.

so now if per ELO the expected score for any two players is for example 0.75 than that means that the game difference in that match should be 0.75*24-12=6 (meaning a routine 6:3, 6:3 type of the score)

if the expected score is 0.35 than the game difference (expected) is 0.4*24-12=-3.6. that means that if a lower ranked player lost like 4:6, 6:7 than he actually 'won' since he performed better than was expected.
I think our disagreement centered around the transformation between tennis score and ELO score... your example illustrates your position well. I'm not convinced that such a transformation (or any similar transformation even if non-linear) is valid in terms of the results it produces, but you've convinced me that it could well be the way USTA does it.

Originally Posted by jmnk View Post
yes, thanks for the suggestion. I'm actually painfully familiar with the algorithm, as I have indeed played tournament chess for quite a while.
I've played some in the past myself, so perhaps if we have any further disagreements we can settle them over a combined chess/tennis challenge Then all we need to agree on is how to weigh the results!
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