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Doug Faust ("Moff Phrim")
Q: What equation determines my rating?
Q: What is the Elo system?
Elo Ratings - Frequently Asked Questions
dlf14@cornell.edu
A: The Elo system, designed by Professor A. Elo, is a way to accurately predict how good players are in comparison to one another, and put this prediction on a reasonable scale. In particular, it predicts how you should do against a given opponent, compares it to how you actually do, and adjusts your rating accordingly.
A: The following equation is used to compute your ratings:
| R = R0 + 32(S - | ) | |
| 10-D/400 + 1 |
R = Your New Rating
R0 = Your Old Rating
S = Your Score in the Game
D = Your Opponent's Rating - Your Rating
Scores are 1 for a full win, 0.75 for a timed win, 0.5 for a true tie, 0.25 for a timed loss, and 0 for a full loss.
Q: Wow, that's a pretty complicated formula! Is there any easy way to figure it out?
A: Yes, there's an approximation formula that can be used to get a rough estimate for your rating. This will be accurate to within a few points for ratings differences of less than 200.
Q: My rating after a tournament doesn't agree with the ratings calculator. What gives?
A: There are a number of things that might have happened to cause this discrepancy. First, make sure that you used your opponent's rating from *before* the tournament, as that's the one that's used. If that doesn't work, it could be that tournaments were updated out of order, two or more tournaments were updated simultaneously, your opponent's ratings were updated after you last checked, your (or your opponent's) command card is illegible, or other such quirks of the system. Decipher has never, to my knowledge, made a raw computational error, so please do not complain that they have.
Q: I am much, much more highly-rated than my opponent in a game. Can my rating go down even if I get a full win?
A: No, your rating will never go down due to a full win, no matter who your opponent is. In these cases (ratings differences of over 700), what often happens is that your rating will go up less than half a point, which will be rounded to zero.
Q: Is it possible to lose points due to a timed win?
A: If the Elo equation predicts that you should do better than a timed win against your opponent, then yes, your rating will go down. In general, this will occur if you're ranked more than 200 points above your opponent.
Q: How does a true tie affect my rating?
A: In general, a true tie causes the player with the higher rating to go down, and the player with the lower rating to go up. A true tie against a player of equal rank will affect neither player's rating.
Q: How does a bye affect my rating?
A: It doesn't. Your rating is only affected when you play a game against a real opponent.
Q: How does getting high or low differentials affect my rating?
A: Differential does not affect your rating. It is only used to determine placing in individual tournaments.
Questions? Comments? Things you think should be in this FAQ? E-mail me at dlf14@cornell.edu.