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Old 11-30-2012, 12:36 PM   #20
LuckyR's Avatar
Join Date: Jun 2006
Location: The Great NW
Posts: 6,392

Originally Posted by jmnk View Post
not sure what sandbagging has to do with this discussion. Are you suggesting that one cannot sandbag by outright losing the match rather than winning it closely? Could you kindly clarify what your point is?

I'm not sure why you think that 3.89 DR is 'slightly above' halfway ranking? Halfway is 3.75. 3.89 is way more that slightly above halfway. Also, next time you make an assumption that is not obvious to anyone but you yourself, please make it clear. Rather than, you know, implying that someone else does not know what 0.5^15 is.
But if you want to discuss a case where someone is indeed at the halfway point, at 3.75. in this case he needs to get his ranking up by .25 points to get bumped. It is significantly harder to earn this .25 dynamic ranking points. Someone who started at 3.89 needs only .11 to get bumped. It really all evens out - you start at the higher DR, you need to play better opponents to move your DR up, but you only need to move up by a small amount. You start at lower DR - it is easier to earn DR points (because you are more likely to meet higher ranked opponents more often) but you need to earn more of those DR points. the system actually makes it all take into consideration which makes it, I don't know, logical?

could you elaborate on what you mean? the expected score takes into consideration dynamic rating, not your NTPR one.
There's no system in the world that would prevent sandbagging. None. Except having all players play in one single category. Do you really want that?

really. you are sure of that. how exactly? do you have some stats? data? dizzlmcwizzl gave you a perfect example of why going by W/L is no better.

If you go by W/L, and a player wants to get bumped - he just needs to play at #3 (assuming this is a 3 players team, singles only). He is likely to play weaker opponents. You are essentially saying that a player beating 3.60 DR players 10 times is vastly better (and should get moved up) than a player who plays 3.80 DR players and has 4/6 W/L ratio. really? that is logical?

(i do think that not separating doubles and singles as far as rating is concerned is the biggest flaw of the system).
Wow, to quote Cool Hand Luke "what we've got here is failure to communicate". I apologize for for being extremely difficult to understand.

A couple of background things:

1- I don't personally believe that how well any player plays the game of tennis can be quantified to three significant digits. Sure the ratings exist, but IMO the science of using rating numbers to predict outcome of matchplay is too poor to justify that level of implied confidence. In my experience the standard deviation of quality of play is so wide that 2 significant digits is suspect, if you don't believe me, ask Lukas Rosol...

2- Regardless of the numerical system, there are players whose numerical rating does not correlate to their quality of play, on purpose, that is they give false information to manipulate the rating. That difference I call Sandbagging and can result in playing matches against better competition who have lower ratings. I was trying, unsuccessfully, to explain that nuance in my last post, first paragraph.

3- I agree that no system will "prevent" sandbagging. As long as people are willing to throw matches completely that will be possible. But this system creates sandbaggers. Using your scenario, the player who is 3.99, will likely always play someone lower rated than they are and thus will go 15-0, as you cite. The system is completely unequipped to deal with the 3.99 who improves their quality of play, yet never "plays up" to 4.5 (as a 4.0). Never gets to demonstrate their improvement against better competition and never gets moved up.

4- You are right that a straight W/L system will incorrectly bump people up who just randomly happened to play a bunch of players at the low end of the scale, you noted that a 3.89 (in the absence of sandbagging) would do so about 2% of the time in a 15 match season. OK you got me, you keep that guy at 4.0, I move him up (incorrectly BTW 2% of the time, your number) to 4.5 Well that 2% of the time in my system what happens? He gets killed playing 4.25s as a 3.89. Next season, he's a 4.0 Self correcting system. At least as a consolation, in a W/L system, no one wonders "why am I playing the 15-0 guy from last year?"

5- The unaddressed issue is the opposite scenario: what about the 4.11 (playing 4.5) who goes 0-15 for the exact same reason the 3.89 goes 15-0? Does that guy get a break? Nope.

6- How better to acknowledge that you do in fact know what a simple mathematical computation is more clearly than by stating: "As you know..."?

7- When you beat someone or get beat 6-0, 6-0 do you think: "I think we were probably mismatched" or "logical score between correctly rated players"? Of course both are possible (what the USTA says), but in your opinion which is more likely?

Ultimately it boils down to this: what is more likely to happen and what is more likely to kill the fun factor of league play: A) a system that thinks it can predict outcomes by rating and only moves players relatively if they behave unexpectedly and beat a "better" player, regardless of how many "lesser" players they smear the court with or B) a system that acknowledges that matchplay is unpredictable for numerous reasons (I agree cheating is one, but a rare one) and figures that the quality of opponents will even out in the end, so a 15-0 guy is likely better than his competition and moves him up?

Either is reasonable but I feel, obviously, that B is less likely to mislabel players, especially in the long haul, as it is self correcting
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