Originally Posted by jmnk
how is it flawed? What is so hard to understand that beating players that are no better than you will not make you move up?
If your dynamic rating is 3.89 (so you are 4.0 player) and you beat a player with dynamic rating of 3.52 (so he is also 4.0) by a score of 6:4 7:6 - how is that supposed to mean you should move up? By NTPR formula, which is based on old and proven ELO rating designed originally for chess (and now used very widely in competition where you can't possibly play --all-- of the opponents: tennis, soccer, on-line games, etc), the expected result is likely around 6:2, 6:2 - so you did worse than expected, which means your ranking went down despite the win.
Now have it happened 15 times over the course of the season and your dynamic ranking (and therefore NTPR ranking at the end of the season) will really go down and not up.
Now, if you want to argue that in tennis we should not care about games won/lost but only about whether someone actually won a match - you may have an argument. Such a system will have its own set of problems, mainly that you will have only two outcomes of any match (a win or a loss) vs. a set of outcomes (depending on games won/lost difference) and therefore there will be way less data for algorithm to crunch. Not that such a system is unheard of - Rogers tennis ranking in Canada is based purely on win/loss (and the 'weight' of the match, some matches are treated more importantly than others). FIFA ranking (which is actually very similar) uses a hybrid method - it cares about both pure win/loss, but also takes into account goal differential (which is equivalent to games differential in tennis).
All of those WTF-like cited cases are likely outliers anyway. The system overall is pretty accurate and serves the purpose. plus it is easy to say 'flawed system' - why don't you propose a better one? I'm sure it will have many edge cases where it will seem illogical (to an untrained eye of course).
I don't think NTRP is entirely based on ELO since ELO only considers win/loss/tie and doesn't use any type of game differential like number of moves whereas NTRP is just the opposite. I don't think most people here who have issues with the NTRP are arguing that it should not incorporate score and dynamic rating differentials into the formula but that it should also incorporate win/loss into it. Hybrid systems which use both exist so it is not beyond the realm of possibility to think that the USTA could also include it.
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Last edited by beernutz : 11-30-2012 at 11:05 AM.