Originally Posted by J_R_B
This is a myth due to one misinterpreted statement by the USTA that is now perpetuated on here endlessly. The fact is that the expected outcome of a match between two players 0.5 apart is not 6-0 6-0. What the statement said is that a 6-0 6-0 match is not unexpected for players with a 0.5 difference. But matches between any two players will have a whole distribution of possible outcomes. If the expected outcome is 6-0 6-0 only 5% of the time (or 1 on 20), then it's still not unexpected, and since there are thousands of matches in the system between players with this ratings difference, seeing some 6-0 6-0 outcomes is normal and expected. They were writing in the context of people who see a 6-0 6-0 outcome and start jumping up and down that that person is automatically misrated or worse, sandbagging. The fact is that the expected outcome (in terms of a mathematical expected value or average) of a match between two players one level apart is probably about 6-2 6-2 or something like that with 6-0 6-0 having enough positive probability that it's not unexpected or unusual to see some in the real results.
I play 4.0. I'm probably near the top of the 4.0 range (I was 14-2 last year but wasn't bumped). I won a match against a 4.0 rated player 6-0 6-0. It was a kid who wasn't bad, but I just happened to get all the games. I also won a match 6-0 6-2 against a 3.5 playing up. The 4.0 kid was a lot better than this guy, but in the course of this match, I happened to lose a couple games. The 6-0 6-0 kid also lost 6-0 6-3 to another college kid who was bumped at the end of the year who can kick my *** all over the court. If we all played a hundred matches, I would probably win 2 or 3 by double bagel against the kid and the other kid would probably win 15-20 by double bagel. That's not how the actual record is, though, and seeing my 6-0 6-0 win in the record is not a sure sign that I am under rated or that my dynamic rating is or should be lower than the other kid who got bumped and who can kick my ***.
You have to be careful about how you interpret statements and expectations keeping in mind that individual match results are a random draw from a distribution and not a fixed measurement of the difference in ratings.
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.