Originally Posted by schmke
So, perhaps a half point difference doesn't have an expected result of 6-0,6-0, perhaps it is 6-1,6-1. You don't disagree that the USTA does have a table of expected results based on rating differential do you? Is that a myth too? At some differential, a 6-0,6-0 result is what is expected and a result short of that will improve the losing players rating and hurt the winning players rating.
You chose not to quote it but I also said a players performance for a given match can vary as much as half a point. This is because you play better/worse on any given day and how you individually match up with an opponent carries far more weight than what some hypothetical rating say should happen.
That said, if your rating is right at the threshold between levels, that means your performance on average indicates you probably beat the lower level players, but lose to the higher level players, more often than not. Of course, if you beat some higher level players and lose to some lower level players, you can arrive at the same point so this is possible.
This also means that if your performance goes up or down a bit from year to year, you will find yourself yo-yo-ing between the levels like the OP cited.
I have heard that the rating system is based on a table of expected results based on rating differential, but since it's not public, no one knows exactly how it works. What I've heard (basically here...) is that the table and the rating calculation are based on total game differentials, not match scores, so it would say something like rating difference 0.50, expected game differential = 8 or something like that. Again, no one but the keepers of the magic formula know for sure and they are sworn to secrecy upon penalty of death. this also means that you can lose matches on the court but win in the rating calculation (consider winning 1-6, 7-5, 1-0, your game score is 9-11).
Of course, you'll beat lower rated players and lose to higher rated players more often than not (as long as the dynamic ratings are accurate), but either predicting or evaluating actual scores is much trickier. Two guys can be a full level apart and play once and the score is 6-0 6-0 and the next time it's 6-4 6-3. The higher rated player will almost always win, but the lower player can get a substantial number of games in any given match. Case in point, again, I am 4.0. I played an open tournament 2 years ago against a 5.0 B rated league player who was a mid 20's teaching pro and former national junior college doubles champ. He is way better than I ever have been or ever will be, but I played the set of my life in the second set and lost 6-1 7-6. This is a match with a rating differential TWO levels apart, and the score still wasn't 6-0 6-0. Even despite the score, I was a long way from actually winning the match, but when it comes to scores, you just never know. Last year in that tournament, I played another mid-20s former college player (D3 ranked school) who would be 5.0 if he played league tennis, and I lost 6-0 6-1.