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| Ratings Diff. | Old Expected | New Expected |
|---|---|---|
| 100 | 63.816% | 57.902% |
| 200 | 76.025% | 65.420% |
| 300 | 85.558% | 72.239% |
| 400 | 92.135% | 78.162% |
| 500 | 96.145% | 83.117% |
| 600 | 98.305% | 87.132% |
| 700 | 99.334% | 90.304% |
| 800 | 99.766% | 92.759% |
| 900 | 99.927% | 94.629% |
| 1000 | 99.980% | 96.037% |
As of January 7th, 2009, the NSA is adopting a new rating system. The new system more accurately estimates how many games a player should win, and it also corrects several long-standing minor issues. Player ratings will not change on the date the new system takes effect, but new ratings calculated after that date will use the new system and not the old system.
The new formula for determining the expected proportion of games
that should be won by a player rated delta points higher than his/her
opponent is 1 - 1/(1+exp(0.0031879*delta)), and is
partially tabulated in the table at left.
The reference implementation of the rating system is the Perl module
Ratings::Elo,
part of the
tsh
software distribution.
The official rating calculator uses this formula and software, and can be used to experiment with hypothetical tournament results.
The bugs present in the old rating software that have been corrected in the new are as follows. Multipliers are correctly computed for players whose ratings start at multiplier boundaries. Performance ratings are computed iteratively, rather than assuming that opponent ratings contribute linearly to expected wins. Feedback points are no longer compounded on acceleration points in any circumstances. The exact expectation is computed for any difference in ratings points, and not just those less than 700 in absolute value.
HASBRO is the owner of the registered SCRABBLE® trademark in the United States and Canada. © 2009 HASBRO. All rights reserved. "SCRABBLE® Brand Crossword Game" is the proper way to refer to this unique group of word games and related properties marketed by HASBRO. "SCRABBLE®" is not a generic term. To use it as such is not only misleading but also does injustice to the company responsible for the trademark's longtime popularity. All we ask is that when you mean SCRABBLE® Brand Crossword Game, you say so.
The SCRABBLE® trademark is owned by J.W. Spear and Sons, PLC, a subsidiary of Mattel, Inc. outside of the United States and Canada.
For more information about SCRABBLE® or the NSA, or to comment on or correct the contents of this page,
please e-mail:
info@scrabble-assoc.com.
For information about SCRABBLE® tournaments please visit our partner organization,
NASPA.
To report technical difficulties in reading this page,
please contact webmaster
John Chew at:
jjchew@math.utoronto.ca