|12-03-2012, 10:09 AM||#1|
Join Date: Apr 2009
NTRP Win-Loss Adjustment Formula
With the new ratings coming out, I thought I'd share what I forwarded to the national USTA office a few years back. The below is a win-loss adjustment formula to be applied to end of year ratings using the current NTRP algorithm and is intended to allow win-loss record to be taken into account when publishing final ratings. Under the algorithm below, the maximum adjustment is .1, but this factor can be set to anything. BTW, the national office rejected the proposal because it would "put too much emphasis on winning and losing", even though I explained the .1 constant (maximum impace of win-loss record) can be lowered as desired. Regardless, here's one way to integrate win-loss into NTRP:
NTRP Win/Loss Adjustment Formula
- Used to adjust end of year NTRP ratings as computed by existing formula
- Max NTRP adjustment for any player not to exceed .10 (.10 used as an example, can be any number)
- Appeal rules for adjusted end of year rated remain as-is
- No adjustment applies to victories over players with lower overall NTRP or losses to players with higher overall NTRP (4.0 defeats 3.5, or 4.5 loses to 5.0)
Variables and values assigned to variables:
X = end of year NTRP rating to hundredth point under existing NTRP formula
Y = adjusted end of year NTRP rating
A = number of wins over players with same overall NTRP rating (.01 adjustment per win; can be any number)
B = number of losses to players with same overall NTRP rating (.01 adjustment per loss; can be any number)
C = number of wins over players with overall NTRP rating above winner’s overall NTRP rating, e.g. a win by a 3.5 over a 4.0 (.02 adjustment per win)
D = number of losses to player with overall NTRP rating below loser’s overall NTRP rating, e.g. a loss to a 3.5 by a 4.0 (.02 adjustment per loss)
X + (A x .01) – (B x .01) + (C x .02) – (D x .02) = Y
For X > Y, if X – Y > .1, then Y = X - .1
For Y > X, if Y – X > .1, then Y = X + .1
Player 1 rated 4.0 during the year has end of year rating of 3.56 using existing algorithm. Unadjusted new year overall NTRP is 4.0 and outside appeal eligibility. Player has win-loss record of 1 win and 4 losses to 4.0s, and a record of 1 win and 2 losses to 3.5s.
Adjusted rating for player 1 becomes: 3.51; overall 4.0; appeal eligible
3.56 + (1 x .01) – (4 x .01) + (1 x .02) – (2 x .02) = 3.51
Since X > Y and 3.56 – 3.51 < .1, final adjusted end of year NTRP rating remains 3.51
Player 2 rated 4.0 during the year and has end of year rating of 3.96 using existing algorithm. Unadjusted new year overall NTRP is 4.0 and within appeal eligibility. Player has a win-loss record of 20 wins and 2 losses, all to players of same overall NTRP rating.
Adjusted rating for player 2 becomes: 4.06; overall 4.5; ineligible for appeal
3.96 + (20 x .01) – (2 x .01) = 4.14; however, since Y > X and Y – X > .10, adjusted rating becomes 4.06 (X + .10). Player becomes overall NTRP 4.5 and outside appeal criteria.
Player 3 rated 4.0 during the year and has end of year rating of 3.75 using existing algorithm. Unadjusted new year overall NTRP is 4.0 and outside appeal guidelines. Player has win loss record of 6 wins and 4 losses, all to players of the same overall NTRP.
Adjusted rating for player 3 becomes: 3.77; overall 4.0; ineligible for appeal
3.75 + (6 x .01) – (4 x .01) = 3.77
Since Y > X and Y – X < .1; adjusted NTRP remains 3.77