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by Matthew Turner
Mon Jun 15, 2020 11:26 am
Forum: 4NCL
Topic: 4NCL Online
Replies: 822
Views: 37212

Re: 4NCL Online

To respond to your comments. An OTB event could use a z score of 4 without collaborating evidence, you would just need a robust appeals process and recognize that there will be a significant proportion of successful appeals. More than a 'significant proportion' I fear. All anyone appealing needs to...
by Matthew Turner
Mon Jun 15, 2020 10:59 am
Forum: 4NCL
Topic: 4NCL Online
Replies: 822
Views: 37212

Re: 4NCL Online

David, You still haven't addressed the question that I posed about what it would take for you to support a ban, rather than initiate one. To respond to your comments. An OTB event could use a z score of 4 without collaborating evidence, you would just need a robust appeals process and recognize that...
by Matthew Turner
Sun Jun 14, 2020 5:23 pm
Forum: 4NCL
Topic: 4NCL Online
Replies: 822
Views: 37212

Re: 4NCL Online

David, That is a great answer and I think I would agre3 with all of that. It is pretty much how the OTB 4NCL and similar events operate. However, I am not sure that you’ve completely answered the first question though. The problem I am posing you is based on incomplete information, so let’s say I fi...
by Matthew Turner
Sat Jun 13, 2020 1:17 pm
Forum: 4NCL
Topic: 4NCL Online
Replies: 822
Views: 37212

Re: 4NCL Online

Roger,
So there are lots of caveats to the answer, but that is not me ducking the question, it is just there are lots of caveats!

If
1. I knew the initial rating was basically accurate
2. It was over enough games/moves
3. I had a sufficiently good way of measuring their performance

Then Yes.
by Matthew Turner
Sat Jun 13, 2020 12:53 pm
Forum: 4NCL
Topic: 4NCL Online
Replies: 822
Views: 37212

Re: 4NCL Online

Roger,
I am not claiming it, it is blindingly obvious. If I have 2 1100 players, one of whom is playing at 1900 they are more likely to be cheating than the one who isn’t.
by Matthew Turner
Sat Jun 13, 2020 12:20 pm
Forum: 4NCL
Topic: 4NCL Online
Replies: 822
Views: 37212

Re: 4NCL Online

Roger, It is strong evidence of cheating isn’t it. The organisers have to decide how to use this information. At Blackpool I would want to investigate further, I might even withhold prize money (temporarily). If the player had a z score of 5 then I would be tempted to ban the player and take my chan...
by Matthew Turner
Sat Jun 13, 2020 10:27 am
Forum: 4NCL
Topic: 4NCL Online
Replies: 822
Views: 37212

Re: 4NCL Online

Justin,
In general I think 5 or 6 games is about the right number to run a valid test. So if i play in a normal weekend congress, my performance would be one occasion. So if Blackpool congress has 400 players they should have one z score of 4 every 75 years or so.
by Matthew Turner
Sat Jun 13, 2020 9:42 am
Forum: 4NCL
Topic: 4NCL Online
Replies: 822
Views: 37212

Re: 4NCL Online

Roger,
Of course you don’t test every move and if you match a computer move you get a high z score and get banned. A typical test might be over 100 useable moves (excluding theory, where one side has an overwhelming advantage and repetitions).
by Matthew Turner
Sat Jun 13, 2020 9:27 am
Forum: 4NCL
Topic: 4NCL Online
Replies: 822
Views: 37212

Re: 4NCL Online

The z score is a measure of how likely a player of a given rating is to play computer moves . A z score of 4 equates to someone performing 800 points above their rating. This should happen naturally 1 in every 31,000 occasions A z score of 2 would be 400 points and one in every 44 occasions. I hope ...
by Matthew Turner
Sat Jun 13, 2020 8:56 am
Forum: 4NCL
Topic: 4NCL Online
Replies: 822
Views: 37212

Re: 4NCL Online

David, That sounds like all good analysis, but by picking a z score of 4.5 what does that actually mean in practice? Let me try to give an example to put you in the 4NCL’s position. Imagine I send you all the games and all the z scores for everybody who has ever played in a 4NCL Congress. I highligh...
by Matthew Turner
Fri Jun 12, 2020 5:28 pm
Forum: 4NCL
Topic: 4NCL Online
Replies: 822
Views: 37212

Re: 4NCL Online

So Chess.com banned 12,000+ accounts last month. Lets say 10% of those were innocent, in the space of a year you would have 15,000 people slagging chess.com off, isn't that going to do reputational damage? It might. I think the percentage is smaller than that though, and I think a lot of people don...
by Matthew Turner
Fri Jun 12, 2020 5:02 pm
Forum: 4NCL
Topic: 4NCL Online
Replies: 822
Views: 37212

Re: 4NCL Online

With chess.com & blitz accounts I think people mostly don’t care that much when caught? At the moment with 4NCL they clearly view as a major offence. That does suggest another way which feels reasonable? You set a fairly ‘high’ false positive rate, but agree that a first offence simply means that y...
by Matthew Turner
Fri Jun 12, 2020 3:54 pm
Forum: 4NCL
Topic: 4NCL Online
Replies: 822
Views: 37212

Re: 4NCL Online

So Chess.com banned 12,000+ accounts last month. Lets say 10% of those were innocent, in the space of a year you would have 15,000 people slagging chess.com off, isn't that going to do reputational damage?
by Matthew Turner
Fri Jun 12, 2020 3:42 pm
Forum: 4NCL
Topic: 4NCL Online
Replies: 822
Views: 37212

Re: 4NCL Online

Ian Thompson wrote:
Fri Jun 12, 2020 2:19 pm
Their priority is to catch all the cheats and not worry about how many innocent players they ban along the way.
Why would they do that though? Surely, it would just make no (commercial) sense.
by Matthew Turner
Fri Jun 12, 2020 3:39 pm
Forum: 4NCL
Topic: 4NCL Online
Replies: 822
Views: 37212

Re: 4NCL Online

David, It is an interesting approach, which seems perfectly reasonable to me. I don't think the number of tests would be halved because each test isn't independent. Clearly there is a much greater probability that you will pass a test in round 9 if you have already passed a test in round 8. So a sea...