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Chess Ratings - How They Work

  • erik
  • | Aug 23, 2007
  • | 136649 views
  • | 483 comments

Like it or not, we ALL have a chess rating. You may not care at all about your rating, or you may be whining every time it goes down in the slightest. You might be someone who plays a game a year, or someone who plays 1,000 a day. Still, there is a number out there that represents how well you play chess. Well, that's the theory, anyway.

To understand chess ratings you have to understand two things: #1 - that you have a TRUE rating that perfectly represents your strength of play, and #2 - that that TRUE rating will never be known and so we have to use statistics to get as close as possible to the truth. I'm writing this article in response to many people who ask about ratings and need a simple explanation of how they work. (I only know about all this because of a recent super-in-depth statistics course I took and my research in building Chess.com!)

There are two main rating systems, and each one has its merits.

The Elo System (used by the United States Chess Federation, FIDE, and many other online chess sites) is popular for two reason - it has been around for a long time, and it is simple. The idea is this: given two chess players of different strengths, we should be able to calculate the % chance that the better player will win the game. For example, Garry Kasparov has ~100% chance of beating my 4-year-old daughter. But he may only have a ~60% chance of beating another Grandmaster. So when playing that other Grandmaster, if he wins 6 games out of 10, his rating would stay the same. If he won 7 or more, it would go up, and 5 of less, his rating would go down. Basically, the wider the spread of the ratings, the higher percentage of games the higher rated player is expected to win. So to calculate a person's rating after playing a few games you calculate the average ratings of his opponents, and then how many games he was expected to win, and then plug it into a formula that spits out the new rating. Simple enough. Well, it turns out, that is maybe TOO simple.

The Glicko System (used by Chess.com, the Australian Chess Federation, and some other online sites) is a more modern approach that builds on some of the concepts above, but uses a more complicated formula. (This only makes sense now that we have computers that can calculate this stuff in the blink of an eye - when Elo created his system they were doing it on paper!) It is a bit trickier than the Elo system, so pay attention. With the Elo system you have to assume that everyone's rating is just as sure as everyone else's rating. So my rating is as accurate as your rating. But that is just not true. For example, if this is your first game on Chess.com and you start at 1200, how do we really know what your rating is? We don't. But if I have played 1,000 games on this site, you would be much more sure that my current rating is accurate. So the Glicko system gives everyone not only a rating, but an "RD", called a Rating Deviation. Basically what that number means is "I AM 95% SURE YOUR RATING IS BETWEEN X and Y." (Nerd Fact: In technical terms this is called a "confidence interval".) If this if your first game on Chess.com I might say, "I am 95% sure that your rating is somewhere between 400 and 2400". Well that is a REALLY big range! And that is represented by a really big RD, or Rating Deviation. If you have played 1,000 games and your rating is currently 1600 I might say "I am 95% sure your rating is between 1550 and 1650". So you would have a low RD. As you play more games, your RD gets lower. To add one extra wrinkle in there, the more recent your games, the lower your RD. Your RD gets bigger over time (because maybe you have gotten better or worse over time - I'm just less sure of what your actual rating is if I haven't seen you play recently). Now, how does this affect ratings? Well, if you have a big RD, then your rating can move up and down more drastically because your rating is less accurate. But if you have a small RD then your rating will move up and down more slowly because your rating is more accurate. The opposite is true for your opponent! If they have a HIGH RD, then your rating will change LESS when you win or lose because their rating is less accurate. But if they have a LOW RD, then your rating will move MORE because their rating is more accurate.

I wish there was some simple analogy to explain all this, but there isn't. It all comes back to this: you have a theoretically exact chess rating at any given moment, but we don't know what that is and so we have to use math to estimate what it is. There are really smart people out there who work on this stuff for a living, and at the end of it all we get to put their proven methods into our code so that we can all enjoy knowing what little numbers next to our name we deserve.

If you want to read more, check out these articles (WARNING - SEVERE NERD CONTENT AHEAD):

- The Glicko System by Professor Mark Glickman, Boston University

- Introduction to Chess Ratings (Elo mostly) on About.com

Comments


  • 4 years ago

    eddysallin

    P.S. CHESS PLAYERS CHEAT ON THEIR RATINGS,IN FACT IT'S  QUITE COMMON.CHECK PROFILE OF YOUR OPPONENTS.IN OVER THE BOARD-LIVE CHESS-YOU HAVE TO WATCH SOME OF THE MORE NIMBLE FINGERED( OH YEA! THEY MOVE PIECES!! ) AS FOR KASPAROV AND MY DAUGHTER. WHO EVER STARTED THAT GOSSIP NEEDS A GOOD WHIPPING. ALSO WATCH OUT FOR THOSE WHO WILL ONLY PLAY WHITE PIECES--ABORT,ABORT!

  • 4 years ago

    gyrhawk

    I don't really care how the ratings or calculated, a more interesting question is when are they calculated.  In standard games an opponent's rating may go up as his other correspondece games finish.  My question is do I get credit for beating the 1200 level player as he was rated in the beginning of the match or for the 1800 level player as his rating was just prior to the end of our match?  I feel this is a good question or I would not bring it up.

  • 4 years ago

    driv4r

    Bogie, I am not sure about theoretical but you can find practical highest and lowest ratings in my blog post here: http://blog.chess.com/driv4r/highest-and-lowest-rating-on-chesscom Wink

  • 4 years ago

    Bogie-

    So what are the lowest and highest theoretical and practical ratings?

  • 4 years ago

    driv4r

    platolag, I have also talked about it a lil in my post below but definitely yes for 4, 5 and 7 moves and defo no for 1 move. I might be wrong here but probably no for 3 moves.

  • 4 years ago

    platolag

    by GRaymond - 8 months ago
    Treviso Italy

    Member Since: Mar 2010
    Member Points: 352

    Question: "is it possible to win points when the opponent resigned after 1 (one), 3 (three), 4 (four) and 5 (five) or 7 (moves) ?

     

    answer is required.

  • 4 years ago

    mufid30

    How exactly to count rating?Please give me the real formulaCool

  • 4 years ago

    palmnut

    how then do  i get my member point and what is my card number

  • 4 years ago

    ChessEngage

    That was actually pretty easy to understand. Thanks!

  • 4 years ago

    1plus1is4

    All your games are unrated so ratings don't change.

    Solid circle=rated

    Doughnut=unrated if u use the graph for seeks

  • 4 years ago

    chessaddictress

    I just joined and I've played about 17 or 18 games here, and my rating is still the same, at 1200.  When does it change?  (Do I have to subscribe?)

  • 4 years ago

    MikeDoyle

    No

  • 4 years ago

    azbloodsport

    I recently had someone obviously let a game time out when I had her nearly beaten.  Had to be the angle of losing fewer points.  But so what?  Her weirdness, not mine.

    My question has to do with whether the number of moves in a game affects ratings.  For example, let's say players with 900 and 1500 ratings are playing against each other.  Does the player with a 900 rating lose fewer points if he loses after 70 moves than if he loses in 10 moves?

  • 4 years ago

    1plus1is4

    as many know from live chess, and those who play computer medium/hard COMPUTERS ARE DISTURBED.Smile

  • 4 years ago

    yttsmd

    If someone had a timeout for whatever reason, the timeout player should be switched to a computer with the same rating as him/her. That is more fair in my opinion. 

  • 4 years ago

    1plus1is4

    NO, if Kasparov plays with only a king and a pawn than he will only beat your daughter 9/10 times :)

  • 4 years ago

    driv4r

    Schroeder59, I think it's 3 or 4 moves by both players, at least in case of timeouts, so it might be same for resignations.

  • 4 years ago

    Schroeder59

    Is there a minimum number of moves for a game to be rated? E.g. if a player resigns after move 1, will the game be rated?

  • 4 years ago

    -rookie-

    Nice explanation.  Thank you!

  • 4 years ago

    sri301

    hi can u pls say me about ratins really i am confused on my rating......

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