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Bridge Hands on Bridgebase. Are the Bridge Hands on Bridgebase truly random?

#61 User is offline   hrothgar 

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Posted 2021-March-20, 12:57

 pilowsky, on 2021-March-20, 12:50, said:

This doesn't sound like a mathematics problem as much as a Turing test problem.
How do you define "interesting" mathematically? Who decides?


I think that you are making things way too complicated.

Mythdoc made a specific claim:

He said that he could take a sip from a cup of tea and determine whether the tea had been added to the cup first or the milk had been added to the cup first (or something like that)

We have plenty of cups of tea
They have labels...
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#62 User is online   pilowsky 

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Posted 2021-March-20, 13:00

 hrothgar, on 2021-March-20, 12:57, said:

I think that you are making things way too complicated.

Mythdoc made a specific claim:

He said that he could take a sip from a cup of tea and determine whether the tea had been added to the cup first or the milk had been added to the cup first (or something like that)

We have plenty of cups of tea
They have labels...


It still sounds like you are trying to make tea in a cracked pot - so to speak.
Skim milk for me, please.
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#63 User is online   smerriman 

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Posted 2021-March-20, 13:02

 mythdoc, on 2021-March-20, 07:13, said:

Just please understand that it is not scientific and doesn’t prove that BBO conditions hand delivery for the two scoring types. It only suggests it.

Done properly, it is entirely scientific.

If I give you 100 sets, 50 that came from IMPs tournaments, and 50 that came from MP tournaments, and you only identify 50% of them, it completely disproves your statement that the difference is obvious.

If you are able to even correct predict, say 70 of the 100 (and you're claiming you'd be able to tell far more than that), that is enough proof for me to show that you are correct, as the probability that happens by chance is negligable.
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#64 User is offline   hrothgar 

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Posted 2021-March-20, 13:10

 pilowsky, on 2021-March-20, 13:00, said:

It still sounds like you are trying to make tea in a cracked pot - so to speak.
Skim milk for me, please.


Take it up with Ronald Fisher...

He's the one who proposed it.
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#65 User is offline   AL78 

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Posted 2021-March-20, 14:09

 mycroft, on 2021-March-20, 09:34, said:


David Stevenson once said approximately, on these forums:

There are three types of bridge sessions:
  • hand-dealt, exciting and swingy: "These hands sure are weird tonight."
  • computer-dealt, exciting and swingy: "Those damned computer hands again."
  • flat, normal hands, hand- or computer-dealt: "Thanks for the game, James."



As far as I'm concerned there are three types of bridge sessions:
1. Below average HCP, struggele to contribute anything, poor score at the end. Feels like a waste of an evening.
2. Below average HCP, pick up hands where I can at least play an active role even if I have to defend three quarters of the evening. Final score anything from poor to reasonable, a fair or enjoyable evening.
3. I declare on at least a quarter of the hands and/or the hands are biased our way, final score is fair to decent. An enjoyable evening.
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#66 User is offline   AL78 

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Posted 2021-March-20, 14:17

 smerriman, on 2021-March-20, 13:02, said:

Done properly, it is entirely scientific.

If I give you 100 sets, 50 that came from IMPs tournaments, and 50 that came from MP tournaments, and you only identify 50% of them, it completely disproves your statement that the difference is obvious.

If you are able to even correct predict, say 70 of the 100 (and you're claiming you'd be able to tell far more than that), that is enough proof for me to show that you are correct, as the probability that happens by chance is negligable.


I believe there is a statistical test, Kolmogorov Smirnov I think, which can be used to test whether two samples come from the same distribution. It is one of those p-value tests where if the p-value is very small, the null hypothesis they are from the same distribution is rejected. If some property of the sets could be quantified numerically, it could be used (e.g. mean HCP North).
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#67 User is offline   hrothgar 

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Posted 2021-March-20, 14:44

 AL78, on 2021-March-20, 14:17, said:

I believe there is a statistical test, Kolmogorov Smirnov I think, which can be used to test whether two samples come from the same distribution. It is one of those p-value tests where if the p-value is very small, the null hypothesis they are from the same distribution is rejected. If some property of the sets could be quantified numerically, it could be used (e.g. mean HCP North).


I think that it might be more appropriate to use FIsher's exact test here (or perhaps one of its more modern antecedents)

There is a reason that I was talking about tea a couple posts back
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#68 User is offline   mythdoc 

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Posted 2021-March-20, 14:56

 hrothgar, on 2021-March-20, 12:57, said:

I think that you are making things way too complicated.

Mythdoc made a specific claim:

He said that he could take a sip from a cup of tea and determine whether the tea had been added to the cup first or the milk had been added to the cup first (or something like that)

We have plenty of cups of tea
They have labels...


No, I made no such specific claim. You interpreted my statement that the differences between the challenges I played on that occasion were obvious as amounting to a claim that I could, and would, do it over and over again like a magic trick. My interest is and has always been that others take a look at these hands and state if they see any patterns. I have no interest in submitting to self appointed lord high interrogators because your lack of good faith is beyond obvious at this point.

 smerriman, on 2021-March-20, 13:02, said:

Done properly, it is entirely scientific.

If I give you 100 sets, 50 that came from IMPs tournaments, and 50 that came from MP tournaments, and you only identify 50% of them, it completely disproves your statement that the difference is obvious.

If you are able to even correct predict, say 70 of the 100 (and you're claiming you'd be able to tell far more than that), that is enough proof for me to show that you are correct, as the probability that happens by chance is negligable.


So, did you look at the hands I posted above? Could be a coincidence, but 3 out of the 4 IMP hands were game score contracts, whereas 4/4 of the MP hands were part score contracts. One of the trends I said one might see to tell one set from another in one of my earlier posts. Doesn’t prove anything, but certainly doesn’t disprove my hypothesis.

Meanwhile this is still a blunt tool to get at the question of whether flat boards are being removed from daylongs.

If you do want to pursue this in good faith, make it public, set up a poll, and post SETS of 12 or 16 board challenges (just declare, non-best hand) of the two types, and ask folks to pick which set is which. Then we might all judge for ourselves.

Or let it drop. I for one am tired of replying to your misrepresentations and playing your gotcha games.
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#69 User is offline   hrothgar 

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Posted 2021-March-20, 15:13

 mythdoc, on 2021-March-20, 14:56, said:

No, I made no such specific claim. You interpreted my statement that the differences between the challenges I played were obvious as amounting to a claim that I could, and would, do it over and over again like a magic trick. My interest is and has always been that others take a look at these hands and state if they see any patterns.


1. You are making a bullshit claim
2. You refuse to do a modicum of work to let other people validate said claim
3. You're too stupid to realize that what I proposed is the same as what you are suggesting with a better experimental design
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#70 User is offline   hrothgar 

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Posted 2021-March-20, 15:21

 mythdoc, on 2021-March-20, 14:56, said:


So, did you look at the hands I posted above? Could be a coincidence, but 3 out of the 4 IMP hands were game score contracts, whereas 4/4 of the MP hands were part score contracts. One of the trends I said one might see to tell one set from another in one of my earlier posts. Doesn’t prove anything, but [i][b]certainly doesn’t disprove my hypothesis.


I didn't bother because I don't trust the way in which the the sets of hands were selected.

As I said before, pre commit to a way in which a reasonably sized sample of future hands can be selected and I'll do so
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#71 User is online   pilowsky 

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Posted 2021-March-20, 15:26

 hrothgar, on 2021-March-20, 13:10, said:

Take it up with Ronald Fisher...

He's the one who proposed it.


Fisher was famously irascible. You two aren't related by any chance? Posted Image
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#72 User is offline   mythdoc 

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Posted 2021-March-20, 15:38

 hrothgar, on 2021-March-20, 15:21, said:

I didn't bother because I don't trust the way in which the the sets of hands were selected.

As I said before, pre commit to a way in which a reasonably sized sample of future hands can be selected and I'll do so


Last I knew, smerriman could access my tourneys and could verify that the two sets were the only two run, as I said they were.

And as I just said, publicly publish sets of challenge hands of the types I specified (just declare, non-best-hand challenges), post them AS A SET (none of this dividing one by one bullshit), have a poll at the top with the following question:

“If, as a supposition, BBO was thought to be selecting sets of hands for competitions involving one human and three robots, to reduce incidence of flat boards, and was doing this both for sets of boards under MP scoring, and for separate sets of boards under IMP scoring, which of these sets (below) would you think is the MP set and which is the IMP set?”

Now that would be very interesting to me.
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#73 User is offline   hrothgar 

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Posted 2021-March-20, 15:43

 mythdoc, on 2021-March-20, 15:38, said:

Last I knew, smerriman could access my tourneys and could verify that the two sets were selected as I said they were.


The issue is why you choose to post these, not whether they exist.

Tell you what, play 8 tournaments tomorrow (4 and 4) and post these...
I'll take a look
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#74 User is offline   mythdoc 

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Posted 2021-March-20, 16:02

 hrothgar, on 2021-March-20, 15:43, said:

The issue is why you choose to post these, not whether they exist.

Tell you what, play 8 tournaments tomorrow (4 and 4) and post these...
I'll take a look


They were the only two I ran, so I should not have said “selected”. But, your offer is exactly what I have been asking, thank you. Almost as if you finally stopped misrepresenting my posts when I insisted upon it, :)

How many boards would you like the challenges to be? You have stated twice how precious your time is, lol. I’ll run them and post the hands sometime tomorrow.
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#75 User is offline   AL78 

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Posted 2021-March-20, 17:05

 hrothgar, on 2021-March-20, 14:44, said:

I think that it might be more appropriate to use FIsher's exact test here (or perhaps one of its more modern antecedents)

There is a reason that I was talking about tea a couple posts back


My knowledge of statistical methods is not complete, and I am not familiar with Fisher's exact test. A quick look on Wikipedia and I see where the tea reference comes from.
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#76 User is online   smerriman 

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Posted 2021-March-20, 19:35

 mythdoc, on 2021-March-20, 14:56, said:

No, I made no such specific claim. You interpreted my statement that the differences between the challenges I played on that occasion were obvious as amounting to a claim that I could, and would, do it over and over again like a magic trick.

To be fair, given the way you said 'obvious' and 'clear difference', the most logical interpretation was that you believed you would continue to be able to see such a difference, even if you didn't specifically state it. Though, you actually did, as far as I can tell, when you said:

 mythdoc, on 2021-March-19, 10:04, said:

As I have said, you will see the difference most obviously in just declare hands

It's not a magic trick, but if there were *any* discernable difference at all, the above test would prove or disprove it - even if you can't predict every single one, you would be able to perform significantly better than statistics would indicate if random.

If you can, you've convinced me. If you can't, then you can at least conclude that your 'intensified suspicions' that raised 'the strong possibility' based on what you thought were discernable differences were all cognitive errors.

 mythdoc, on 2021-March-20, 14:56, said:

So, did you look at the hands I posted above? Could be a coincidence, but 3 out of the 4 IMP hands were game score contracts, whereas 4/4 of the MP hands were part score contracts. One of the trends I said one might see to tell one set from another in one of my earlier posts. Doesn’t prove anything, but certainly doesn’t disprove my hypothesis.

The main reason I stopped playing MP + IMP daylongs a while ago was because the number of flat boards made it futile in aiming for a top score - I found it too frustrating that they were largely dependent on luck vs skill (the complete opposite of your experience). But you're right; a one-off example doesn't prove or disprove anything; a large set does for the reasons mentioned above.
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#77 User is online   smerriman 

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Posted 2021-March-20, 20:07

 mythdoc, on 2021-March-20, 15:38, said:

Last I knew, smerriman could access my tourneys and could verify that the two sets were the only two run, as I said they were.

I can't - barmar has a script set up that emails me results by participants during BBO events, but not in general.
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#78 User is online   smerriman 

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Posted 2021-March-20, 20:47

By the way, I looked at the hands you posted.

You're saying set 1 was from an IMPs challenge, where hands are biased to make them have more IMP variance?

Board 1 - both beginners and experts alike would take a flat 10 tricks. No decisions to be made.
Board 2 - given the friendly trump break, both beginners and experts alike would take a flat 11 tricks. No decisions to be made.
Board 4 - given the club lead, both beginners and experts alike would take a flat 9 tricks. No decisions to be made.

I guess it's possible an absolute beginner might find a way to go down 3 on board 3, but everyone else should go down 2 and score a fraction of an IMP at most.

As for the MP set:

Board 1 - no decisions
Board 2 - after the first two tricks I guess the only decision is how to play trumps, but it turns out everything you try works equally, so no variance
Board 4 - again there's only one way to play this at any form of scoring

Board 3 appears to be the only one of the 8 boards where you actually have anything to think about.. still looks pretty flat but even if there's a bit of variance, it'll affect both forms of scoring equally.

Perhaps it wasn't the greatest example for demonstrating your point :)

If you're no longer looking at variance, but think that the chances of a game being makeable is more likely in IMPs than MPs (you referred to the number of games and partscores, rather than variance), then that can be analysed.. but let's stick to one thing at a time.
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#79 User is online   pilowsky 

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Posted 2021-March-20, 20:53

I just played a 16 board tournament.
Every single board had a hand with a singleton or a void - nine had more than one.
Therefore the Earth is flat and Santa Claus is green.
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#80 User is offline   Douglas43 

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Posted 2021-March-21, 06:22

I believe Santa Claus was traditionally portrayed in a green costume before a commercial organisation reclothed him in corporate colours, so Pilowsky could be onto something...
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