IGS rating system
On April 1st, 2005, IGS changed its rating system to more accurate and more clearly defined. Several steps are being taken to achieve these goals.
- ratings will be calculated at the completion of each game rather than once a day
- ratings will have an indicator for strong players at each rating, signified by appending a '+' to the player's rating (3d+ vs 3d)
- unrated players will be indicated by having a '?' appended to their rating (3d? vs 3d or 3d+)
- ratings changes will be 'protected' by a guard band which introduces a measure of hysteresis into the system
- the effect of a single game at the correct handicap on each of the players will be symmetrical, increasing the winner's rating by 100 points and decreasing the loser's rating by 100 points.
- ratings will have a lower bound of 22k
- players below 22k will be placed into a 'Beginners Class'
easter: The 27 mars 2007 a modification took place. The new lower bound is 17k. The rating classes from 8k+ to 22k was affected and points were added according to a sliding scale to make them fit in the interval from 8k+ to 17k.
EdwardHammerbeck: Just to clarify a few points regarding the new rating system. If you have 20 rated games, but do not have 5 wins in rated games, then you will not have a numeric rank. You will have a 'BC' rating until you have 5 wins in go games. This was confusing to me until I experienced it myself. So if you have 20 rated games, and you have 5 wins among these rated games or other non-rated games, then you will have a rank of 20k or 20k+ or 3d or 3d+, or whatever your rank is. If you have 20 rated games but less than 5 wins out of all your rated and non-rated go games, then you will have a rank of BC. Wins in any type of standard go game count toward getting you out of the beginner class even if they come from smaller board sizes, e.g. 9x9, or from players with whom your game would otherwise not count as rated, e.g., ? or BC players. In terms of the Beginner Class win requirement, a win is a win.
If you have less than 20 rated games, you will be given a provisional rank based on what you entered using the "rank" command or the system's best guess as to your rank. These provisional ranks will be followed by a question mark, "?". In other words, your rank will look like this: 22k?.
To sum up, a typical newbie's progression might look like this:
- Register for a new account and use rank command to seed your rank at 22k. Rank shows as 22k?.
- Play 20 rated games and lose a lot. Your mentor lets you win a couple 9x9 games. BC win count goes up to 2. Rank = BC.
- Play some more. Win some, lose some more rated games. BC wins finally reach 5. Rank = 22k or whatever. Congratulations. You no longer have a provisional rank or a beginner's rank. You have a real, honest-to-goodness rank and now go up and down like everyone else on the server.
The whole point, from what I understand, is that the rating algorithm needs a certain minimal amount of data to get a good estimate of how you rank compared to your peers. Twenty rated games isn't good enough because you could (like me) lose all 20. You need to have some wins in there to say, "OK, she's better than this guy and this guy but not this guy.... She's 20k+."