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Old 01-23-2013, 09:55 AM   #35
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Originally Posted by schmke View Post
I agree that the algorithm is not necessarily the best. I'd certainly do some things different if I was doing it from scratch. Tell me more about updating a rating after every set though. If you were supposed to win a set 6-4 but win 6-2, the participating players ratings are updated and you are supposed to win the 2nd set 6-3 or something like that?
Not exactly; ELO (in its pure form) is binary; what would be important is who won the set, and not the set score. So the rating does not set an expectation for the set score, rather the difference in player ratings determines the starting probability of each player winning the set. Ratings adjust after each set based on who won/lost the set.

This method would be superior in considering scores such as 7-6, 1-6, 1-0.

As I understand it, in the current system adjustments are based on total number of games (perhaps I am wrong?). So in this example, the game score is 9-12, and player A is determined to have 'lost', although of course he won the first match!

The binary ELO per set method would recognize this as 2 sets won for player A, and one set for player B.

The primary drawback is of course not being able to differentiate between for example 6-1, 6-1, and 7-6, 7-6.

ELO can be adjusted to consider margin of set score in addition to won/loss, but I'm not even sure that would be better. I think scores within a set are often not representative of relative strength anyway. Also, comparing with the current algorithm, the current algorithm already has a similar (and actually more significant) flaw in that the third set is just recorded and considered as 1-0.

Originally Posted by jmnk View Post
Fair enough. Do you have an idea for a different ranking algorithms? Let's discuss it.

And USTA algorithm --is-- based on ELO principle. and it --does-- adjust the rating after every match (granted, not after a set but after a match). It adjusts player's dynamic rating. Your period-end ranking is essentially your dynamic ranking at the end of the ranking period, rounded to 0.5.
USTA algorithm is not ELO, although of course they share the principle of adjusting ratings after each set/match. I meant actually applying the specific ELO methodology and algorithm. Most significantly as I've noted above, pure ELO is binary and considers win/loss rather than score, and that's what I would implement for starters.

I've implemented this for other things and think it would be a good fit for tennis.
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