Ranks and rating - online-go/online-go.com GitHub Wiki
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The OGS ranking system
A novice go player who just learned the rules will not be of the same strength compared to a player who has been playing for years. In order to distinguish between different players, ranks are assigned to individual players. This helps players find matches with people of appropriate skill. The strength of a go player is rated according to their results in competition with other ranked players. You would expect that a player's rank increases when they win a game and decreases when they lose a game. However the rating system OGS uses (Glicko 2) that works in a different way.
You have probably noticed that sometimes your rank goes down after you have won a few games and vice versa. This is confusing and feels illogical. OGS rating system is based on a 15 game sliding window. This sliding window only takes into account games that are played on the regular boards (9x9, 13x13 and 19x19). Other board sizes, such as 25x25, 15x15, 12x7, etc., are not used in calculating your rank. Also other forms of fantasy go games, such as Diplomat Go, are not used to ascertain your rank. All types of games (blitz, normal and correspondence) are included in calculating your rank.
What is a 15 game sliding window?
The calculation of your rank is based on the results of your last 15 games. When you finish your 16th game, the first game used in calculating your previous rank falls out of the window and is replaced by the result of your 16th game. If that first game was a good result for you (winning of a higher ranked player) and it is replaced by a less good or bad result in your 16th game (winning, losing to an equal or lower rated opponent), your rank will drop. Of course the opposite is also true.
An example
Let me clarify it with an example. Suppose a machine automatically places crates on a conveyer belt and that this belt only has place for 5 crates. When the machine places the sixth crate, the first one has fallen off the belt. Not all the crates have the same weight. In the following table you see the crates' weight that are on the belt. With each new crate that is placed on the conveyor belt, the total weight on the belt changes.
| 1. | 2. | 3. | 4. | 5. | 6. | 7. | 8. | Total |
|---|---|---|---|---|---|---|---|---|
| 20 | 16 | 22 | 19 | 25 | 102 | |||
| 16 | 22 | 19 | 25 | 13 | 95 | |||
| 22 | 19 | 25 | 13 | 27 | 106 | |||
| 19 | 25 | 13 | 27 | 18 | 102 |
If you replace the crates total weight by ranking, you see what is happening.This is very simplistically why rankings sometimes change in a rather unexpected way.
Miscellaneous
- When you start playing at OGS you have no ranking yet, so your rank (next to your name) is displayed as a question mark ("?"). The system has no information on your actual ranking yet. This will quickly change if you play several matches with ranked players (usually about 5 are needed to ascertain your rank).
- The rating is calculated in Glicko points. To make it easier for you the Glicko-rating is converted to the traditional kyu and dan grades. When you just have learned the rules and started playing, your rank usually starts at 25k and as you get better you can eventually climb to 1k (which is the highest kyu rank). If you surpass this you can become a dan (a master rank) and starting from 1d climbing up to a maximum of 9d.
- Rating systems are never perfect. On the OGS forums there are literally dozens of topics dealing with rating. The OGS rating system is continually under review, but change is inevitably slow. So every once in a while you will come across a topic like I won three games in a row, but my ranking went down. How is this possible?
- Ranking refers to a position on a scale (your ranking is 1700 and that means 9k). Rating refers to a classification of someone based on a comparative assessment of their performance.