Answers.Body: <p>Your understanding is correct, at least for the Elo system (and systems derived from it).  These systems only make adjustments to a player's rating based on results against other players that they've actually played against.  They don't make any explicit attempt to extrapolate a player's performance based on how that player's performance compares against other players that their opponents have played (but whom the player under consideration has not played).</p>
  <p>You can find a description of the US Chess rating system <a href="https://new.uschess.org/sites/default/files/media/documents/the-us-chess-rating-system-revised-september-2020.pdf" rel="nofollow noreferrer">here</a>, which describes the computations that are done to adjust a player's rating after an event in which they've played.</p>
  
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Answers.CreationDate: 2022-02-02T20:30:12.113Z
Answers.Text: I was thinking "K" could be higher when playing someone with a low  level of connection between the players.
Answers.UserDisplayName: Ian Ringrose
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Answers.Text: One could potentially try to atone for a multitude of sins via the K factor.  As used in Elo-like systems, though, it's strictly a measure of how volatile a player's rating is, and only information about that player is used to choose K.  The general assumption is that the ratings of low-rated players may change quickly, but that that high-rated players probably won't get worse (or much better) quickly.   It's further assumed ratings based on a small number of games may change quickly (the rating system doesn't know much about the player yet), while long-established ratings are more stable.
Answers.UserDisplayName: patbarron
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Answers.Text: There is already a system in US when new people who do a lot better then expected get their rating increaed more.   Maybe also a bonus when doing a lot better then expected agaist playing who are not well connected to you but are well connected to many other players.
Answers.UserDisplayName: Ian Ringrose
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Answers.CreationDate: 2022-02-02T20:24:29.033Z
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Answers.UserDisplayName: patbarron
Body: <p>Given the issues with rating people who mostly play within a cluster that contains few people who play outside the cluster, I was expecting rating systems to take more notice of results against another player who was well connected to many different clusters of players.   Yet they seem not to. What am I missing in my understanding?</p>
  
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Comments.CreationDate: 2022-02-03T04:04:51.443Z
Comments.Text: I would guess that this hasn't been a main focus because in many scenarios that is unlikely to happen. However, there would be some uses cases of course, so it might be interesting to try and model it.
Comments.UserDisplayName: koedem
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Comments.CreationDate: 2022-02-03T07:10:38.637Z
Comments.Text: tl;dr They cope badly
Comments.UserDisplayName: Evargalo
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Comments.CreationDate: 2022-02-03T11:25:53.757Z
Comments.Text: @koedem I think the US creates problem for international rating systems by most mid range US players not playing in a international rated match until they have become very experienced players.    There is also issues that is clearly easyer to get 2500 in some countries then others.
Comments.UserDisplayName: Ian Ringrose
Tags: <rating>
Title: How do rating systems cope with clusters of players who nearly always only play people within their cluster?
ThreadText: # How do rating systems cope with clusters of players who nearly always only play people within their cluster?
  
  (Asked by: username_0 on 2022-02-02)
  
  Given the issues with rating people who mostly play within a cluster that contains few people who play outside the cluster, I was expecting rating systems to take more notice of results against another player who was well connected to many different clusters of players. Yet they seem not to. What am I missing in my understanding?
  
  **Tags:** rating
  
  > **Comments:**
  > **username_1**: I would guess that this hasn't been a main focus because in many scenarios that is unlikely to happen. However, there would be some uses cases of course, so it might be interesting to try and model it.  
  > **username_2**: tl;dr They cope badly  
  > **username_0**: @username_1 I think the US creates problem for international rating systems by most mid range US players not playing in a international rated match until they have become very experienced players.    There is also issues that is clearly easyer to get 2500 in some countries then others.  
  
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  ## 1 answers
  
  ### Answer by username_3 on 2022-02-02. Score: 4 | Accepted answer
  
  Your understanding is correct, at least for the Elo system (and systems derived from it). These systems only make adjustments to a player's rating based on results against other players that they've actually played against. They don't make any explicit attempt to extrapolate a player's performance based on how that player's performance compares against other players that their opponents have played (but whom the player under consideration has not played).
  
  You can find a description of the US Chess rating system [here](https://new.uschess.org/sites/default/files/media/documents/the-us-chess-rating-system-revised-september-2020.pdf), which describes the computations that are done to adjust a player's rating after an event in which they've played.
  
  > **Comments:**
  > **username_0**: I was thinking "K" could be higher when playing someone with a low  level of connection between the players.  
  > **username_3**: One could potentially try to atone for a multitude of sins via the K factor.  As used in Elo-like systems, though, it's strictly a measure of how volatile a player's rating is, and only information about that player is used to choose K.  The general assumption is that the ratings of low-rated players may change quickly, but that that high-rated players probably won't get worse (or much better) quickly.   It's further assumed ratings based on a small number of games may change quickly (the rating system doesn't know much about the player yet), while long-established ratings are more stable.  
  > **username_0**: There is already a system in US when new people who do a lot better then expected get their rating increaed more.   Maybe also a bonus when doing a lot better then expected agaist playing who are not well connected to you but are well connected to many other players.  
  
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