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How does the rating system work on here?

Asked by Clarkey rating ratings glicko-2 ranking faq Viewed 69721 times, last updated
52
My (or my opponent's) rating changes very dramatically after a game and the numbers don't seem to add up. How are ratings calculated?
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Ratings are calculated using the Glicko-2 rating method developed by Mark Glickman. This is a very popular rating method, and is used by a significant amount of chess organisations (FIDE being a notable counter-example, as they still use the dated Elo rating system).

Fundamentally, Glicko ratings use "confidence intervals" when calculating and representing your rating. When you first start using the site, your rating starts at 1500 ± 700. The 1500 represents your rating, and the 700 represents the confidence interval.

Basically, the system is 90% sure that your rating is somewhere between 800 and 2200. It is incredibly uncertain. Because of this, when a player is just starting out, their rating will change very dramatically, potentially several hundred points at a time. But after several games, the confidence interval will narrow, and the amount of points gained/lost after each game will lessen.

Another thing to note is that the confidence interval changes over time. If you win or lose many games (or rather "points") in a row, the confidence interval will increase allowing you to gain/lose points points more rapidly. This is because a winning/losing streak means that you are incorrectly rated/seeded and the rating system should compensate for that.

"Why use 1500, and why use Glicko in the first place? I much preferred it when the ratings started at 1200 and Elo was used; it was far more accurate with FIDE ratings."

1500 is used because it is the figure specified by the Glicko-2 documentation that can be accessed here: www.glicko.net/glicko/glicko2.pdf

The change from Elo to Glicko was a conscious decision. The main issue with Elo was that ratings moved too rapidly. Against a player of equal strength, it was possible to gain or lose 100 points in less than a handful of games. There were other issues as well, such as most players (of vastly different strengths) being bulked together near 1200. This was incredibly problematic.

After changing to Glicko-2, players have been far more evenly spread-out within the rating ranges, making it far easier to find an opponent of appropriate strength. It is also far easier to maintain a rating.

"But ratings are far higher compared to other sites and organisations such as FIDE, USCF, the ICC, etc... What's up with that?"

It is best not to think of ratings as absolute numbers, or compare them against other organisations. Different organisations have different levels of players, different rating systems (Elo, Glicko, Glicko-2, or a modified version of the aforementioned). These factors can drastically affect the absolute numbers (ratings).

It's best to think of ratings as "relative" figures (as opposed to "absolute" figures). By this I mean: within a pool of players, their relative differences in ratings will help you estimate who will win/draw/loss, and how often. Saying "I have X rating" means nothing unless there are other players to compare that rating to.
Patrizsche commented :
u2krazie commented :
Does the rating system here have a floor?
Clarkey commented :
I don't believe there is a rating floor.
chunkymonkey commented :
I'm no maths expert, but from a layman - the system used won't give you 'a floor' - unless you want to call the floor '1500'. At any point whilst playing, there will be somebody with a 'lowest' rating and somebody with a 'highest' rating. Those values are not bounded but are usually within about 2800 and 800 ish.......
If you are familiar with bell curves, the average here is normalised at 1500. That doesn't mean that the average person plays at 1500. It means the average of everybody playing has been set at the arbitrary figure of 1500. Somebody from math want to jump in and explain it better or more better or even accurately? :D Is there an absolute minimum and maximum rating -
Isaiah4031 commented :
I recently had the experience of playing a friend w/ a rating less than 1000... When I won he lost a point and I gained nothing... This indicates to me (perhaps counter-intuitively) that there is a floor [albeit a mushy morass of one]. Eventually the gap becomes so great that the lower ranked person is not penalized for attempting to improve through practice.... Hopefully, the 'higher ranked' person isn't gigged too badly for playing a range of people.
chunkymonkey commented :
Yup - that's it! I think (to be corrected no doubt) all the Glicko system does is try to accelerate the process of fitting a player to the bell curve. So that means- if you are a new player - your rating is 1500 but there is huge uncertainty about it. Lose a game - your rating gets hit big time - likewise if you win - it goes up big time! Then, as you play, the score will settle as confidence grows.....
That paper I just linked to describes the way the formula works precisely but I think that's the jist of it....
chunkymonkey commented :
Ok - the question again - is there a theoretical floor (or ceiling) rating with Glicko 2 - if so what are they?
chunkymonkey commented :
Ermm - I've just given it more thought - I don't think he ratings here necessarily do fit a bell curve - for good reason.... Clarkey - have you got a mathematician on hand?
msm7 commented :
Thank you very much for the reply
CHTAN commented :
Thank You Mr.Clarkey. I had found the answer to this question since I join lichess.org.
virginaheatrush commented :
It could be Ms Clarkey
HMZ306 commented :
thank you for explication
but i want to understand what is the temporary rating with the sign '?' and what is the reason of usng it?
if someone can explain
Clarkey commented :
The question mark stands for "provisional". If your rating is 'provisional' it means that it's a rough estimate and likely to change dramatically. It means it is not an accurate representation of the player's ability.
seven_samurai commented :
Clarkey, I've only been at the site for a few months, but have played online for about twenty years. Thanks to the team for the great work and design you offer, and for the abundance of features. Lichess is now my home site, after exploring many over the decades dating back to Caissa's Web.
Francesco_Super commented :
Excellent answer!!! I voted it (+1)
yhete commented :

Absolutely incredible answer, thank you so much!
> Basically, the system is 90% sure that your rating is somewhere between 800 and 2200

Great answer and great approach, but this explanation of confidence intervals is actually wrong and would be more suited for bayesian credible intervals. From wikipedia:

> The confidence interval can be expressed in terms of a single sample: "There is a 90% probability that the calculated confidence interval from some future experiment encompasses the true value of the population parameter." Note this is a probability statement about the confidence interval, not the population parameter.
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