5

Context : while playing against a complete stranger that hide its rank/level.

I feel like it would be possible to guess the opponent's strength by analyzing its responses to tesujis, probes, etc. during the game.

Is there some patterns (or moves or errors) that indicates that a player has or has not reach a certain plateau ?

If it's the case, is there any on-line resource on the subject ?

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    I'm not sure if there is a real answer to this question. Skill in Go is not a linear progression: You may be great at tesuji, but your fuseki may be terrible - or the other way around. And in particular, you often don't know that you're bad at something (thus cannot judge others correctly on that topic). --- That being said, I am currently working on a project which involves gathering evidence on this very issue, so maybe there is some kind of answer, after all. – mafu Feb 18 '16 at 18:25
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    @mafu "There is no way to do this, and here's why" is actually an answer to the question, though! – Cascabel Feb 24 '16 at 13:35
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    I’ve heard the odd anecdote about players not letting on about how strong they are or being asked to comment on a professional game which they were told was by weak amateurs. They back up the idea that it is not as easy as you might think. The main thing is that if one cannot understand why a play is good it will not help you to estimate the strength. And go is full of surprising switches of emphasis and subtle timing. The one giveaway is when one can be absolutely certain that a move is forced and a player does not see it, but it is hard to estimate the size of many threats. (@mafu, too) – PJTraill Nov 23 '17 at 20:30
5

In addition to the way proposed by Nathan, I would like to add a few further ideas.

Winning percentage

One simple way to judge the relative strength of two players is to look at their mutual game history (if it is large enough, of course!) and consider the percentage of won and lost games. For instance the EGF rating system has this property:

This setting gives about 30% probability for beating a 1 grade stronger opponent.

So if one players wins only 30% of the games, we may assume he is one stone weaker. Other percentages can be translated via their formula.

Of course, a large number of games between the two players is required. Also, relative strength is not transitive: It may well be that player A usually beats B, B usually beats C, and yet C beats A more often than not.

Score

Historically, the average score difference in (sufficiently many) even games is a good indicator.

One stone difference in strength equals two komi, and komi is usually around 6-7 points. So, for instance, if one players wins by around 26 points on average, we may assume he is 2 stones stronger.

Obviously, this approach suffers from resignations - the players would need to continue lost games until scoring. simply applying a threshold seems to be impossible in general, and may only be useful in specific instances.

Judging moves

I was interested in seeing how accurately we can judge the level of Go players from their moves and created a website for this purpose: https://kyudan.net

It displays the first 100 moves of an anonymized game. Once you submit your estimation of the respective level of the players, their real rank is displayed. All players are dan level up (so the options rank from 1 dan to 9 dan only). More information about the process are described here.

When I last looked, there were more than 2000 results submitted by more than 100 people. There was a significant (from appearance, I did not really number crunch this) difference in estimation accuracy between different judges. The most accurate people were often within 1 - 2 stones of the real ranks, but on average people were off by 2 - 3 stones. You can see my personal results here.

Considering that simply always selecting "5 dan" will lead to being within 4 stones of the correct answer, it seems apparent that judging player level from a single game is not easy for most of us.

  • This is a fantastic answer ! You've done a great job ! – Kii Nov 30 '16 at 15:08
7

Probably the best way to gauge a player's strength (aside from playing against them of course) is to present them with Tsumego of varying difficulties. From Sensei's Library:

Tsumego, a Japanese go term adopted into English, are problems mainly about life and death, but also about ko, capturing races, cutting, connecting, etc. As a rule they are local problems, but a few involve the whole board.

There are many published collections of tsumego, or life-and-death problems, many in Asian languages but increasingly many in Western languages. Many collections are available on the internet. SL also has a growing collection of go problems.

Most professional players and top amateur players agree that solving tsumego is the best way to improve.

Sensei's Library has a plethora of tsumego from a variety of sources.

Personally, I've also used GoProblems.com a lot to improve my own skills. I like that they try to associate individual tsumego with what rank should be able to solve them. They also have an incredible number to choose from. As of this posting they claim to have 11,196 problems.

  • Sorry I wasn't clear. I meant how to know their strength during the game. Thanks for the answer anyway ! – Kii Feb 18 '16 at 18:17
  • And how would you weight its strength during a game ? – Kii Feb 18 '16 at 18:21
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    My mistake. It's tough to say in-game how good a player. I agree with @mafu that different players have different strengths; there's no set standard of "knowing these tesuji and these joseki makes you a 12 kyu." Analyzing their play holistically (use of tesuji, use of sente, responding to ko, etc.) may give you a sense, but it's especially difficult to judge against opponents better than you. That said, one VERY general rule of thumb is that every 20 point difference in score represents a difference in rank. i.e. - if your opponent wins by 60 points, they're roughly 3 ranks better than you. – Nathan Thompson Feb 18 '16 at 18:59
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    @NathanThompson The score difference is a very good point (from many games, not just one, of course). I've heard of it with 7, 10 or 14 points instead of 20, it seems everyone uses a different metric there. Considering that 1 handicap stone equals 2 komi in theory, something around 14 sounded most reasonable to me, but I've never really thought about this. – mafu Feb 29 '16 at 18:16
  • @mafu could you write an answer, I'll validate it – Kii Nov 30 '16 at 13:59

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