3. Your win-loss record (ties count as a half a win.)
The ratings rating program first figures out how many games you should have won. This is known as your “Expected Wins.” The ratings rating program uses your intial rating and the ratings of all your opponents to perform this calculation. It then subtracts your Expected Wins from your actual number of wins to get the difference. It then multiplies the difference by your K value (see below) to calculate your rating change. If you won fewer games than what was expected, then the difference will be negative meaning you lose rating points. If you won more games than expected, then you will gain ratings rating points.
The K value, or sometimes called the Multiplier, is usually 20. However players with less than 50 tournament games will have a higher K value, the idea being this helps accelerate them to their “proper” rating. Also, once a player's rating goes above 1800 or 2000, their K value drops to 16 or 10, respectively.
The ratings rating system also implements Acceleration and Feedback points. If someone does exceedingly well - that is gains a lot of ratings rating points - they are awarded Acceleration points and their opponents are awarded Feedback points. The underlying assumption in this case is that the player was “underrated” going into the tournament and they should have been rated higher. Hence the Acceleration points. Furthermore, because they were underrated, their opponents probably lost more (or didn't gain as many) points than they would have, hence the Feedback points.
This leads to the common question “Is my rating an indication of how good a Scrabble player I am?”
In a pure mathematical sense, your rating is essentially your overall winning percentage weighted by your opponents’ weighted winning percentages. It does not directly measure your word knowledge, board vision, time and rack management skills or other attributes required to be a good Scrabble player.
On the other hand, the object is to win the game. The better players will tend to wim more games, and the ratings reflect that. remember Remember that Scrabble has a certain amount of inherent randomness, so in any given game, the lower rated player has a chance. And upsets do happen.
I hope this article gave you some insight into how the ratings rating system works. I plan on publishing additional, more technical articles in the future. If there is something specific you would like to see documented, or have questions / comments, please feel free to drop me a note.
[[Jim Hughes]]
Managing Director, [[Ratings and Recognition Committee]]