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Everyone sits South in BBO Is there bias in the way that hands are dealt in BBO

#1 User is offline   pilowsky 

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Posted 2020-July-31, 20:50

Like a bad conspiracy theory, or a piece of Soviet-era propaganda, Some questions come up very frequently on this Forum, so I created a small experiment to answer some of them.
I set up an IMPS table in the Prime area with a robot at each seat. I then let the robots play 6 sets of 12 hands - 72 boards (see Figure).
Each hand is also played elsewhere in BBO world against robots and with a human in one seat. The human is generally sitting South.
Here are the results:

Posted Image

Is there bias in the way that BBO deals the hands?
If this were the case then after playing 6 sets of boards one of NS or EW would have a significantly higher number of IMPS. Chi-square test is negative. The sum of wins and losses is equal to 0 therefore no bias exists.

Which is the best seat?
There is no bias so no seat is better than any other, but I recommend that you wear a mask and avoid television.

Which robot is the best partner?
This study was conducted using advanced robots. It would be interesting to see how much quantitative difference there is when pitting two advanced robots against two basic robots, or playing a 'team of three'.

Other conclusions.
There is a bias towards South in the Bridge community for historical reasons [1] and most players in the Prime area choose to sit South. BBO perpetuates this by seating players South in 'Best Hand' tournaments. Perhaps players in Prime and elsewhere jump for the South seat in the expectation that there are hands floating about in the ether cast adrift from 'Best-Hand' tournaments, and that if they sit South they will benefit from this. Like panning for gold in the effluent from a gold mine.
This seems not to be the case.
I still like to sit South though.
Of course, it doesn't help that whichever seat you choose, you are always at the bottom of the screen. Coming from the Southern hemisphere I'm used to it, but some in the North, East or West may find it tough going.


[1] "It was George [Kaufman] who pointed out that you could always hold good cards merely by sitting South. 'No matter who writes the books or articles,' he said,
South holds the most terrific cards that I ever saw. There is a lucky fellow if I ever saw one.' Ever since then, I have always sat South.
That is the secret of my success, and I pass it along to you for whatever it is worth." Charles Goren




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#2 User is offline   hrothgar 

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Posted 2020-July-31, 21:52

No
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#3 User is offline   AL78 

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Posted 2020-August-01, 02:01

I have recorded my average HCP playing in my virtual club on BBO. I nearly always play North or East. There was initially a bias towards me picking up sub-average HCP over a session, and more so my partnership picking up sub-average HCP, but this has gone with having better than average HCP over the last four sessions. My conclusion so far is that what feels like a bias at the time is really a temporary streak, and the streaks can go both ways. Streaks are routine even in completely random systems.
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#4 User is offline   pilowsky 

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Posted 2020-August-01, 02:24

Correct. Just thought I would put it to rest with actual evidence. Even though it should be obvious.
non est deus ex machina; även maskiner behöver lite kärlek; Wanneer elk gezegend ding dat u vasthoudt is gemaakt van zilver of van goud, verlangt u naar eenvoudig tin; Lätt som en plätt; uczciwość jest jedyną wartością
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#5 User is offline   awm 

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Posted 2020-August-01, 02:43

While I don’t think there’s a bias in the deals, there does seem to be bias in the direction better players / more established pairs sit in the main bridge club.

Practicing with the same two pairs over several weeks, we have noticed that the pair sitting E/W normally “wins” because the E/W field is substantially weaker than the N/S field.
Adam W. Meyerson
a.k.a. Appeal Without Merit
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#6 User is offline   paulg 

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Posted 2020-August-01, 03:10

Some club members have told me that they prefer South because it looks more natural to have North at the top of the screen, West on the left and East on the right. This seems more true when they first start playing on BBO.

At my club in real-life, the stronger pairs sit North-South through preference since they control the boards and the Bridgemates and don't trust the weaker players to do so. It may mean that they are less likely to win (for the reasons outlined by Adam) but this seems less important!

This element of control for N/S probably transfers subconsciously from real life to BBO, even though it does not exist.

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I don't work for BBO and any advice is based on my BBO experience over the decades
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#7 User is offline   hrothgar 

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Posted 2020-August-01, 03:38

View Postpilowsky, on 2020-August-01, 02:24, said:

Correct. Just thought I would put it to rest with actual evidence. Even though it should be obvious.


But you haven't

You sample size is grossly insufficient and a bunch of the claims that you are making distract from your main point.

For example, if you want to show that HCPs are balanced, show the distribution of HCPs.
Don't use the number of tricks taken in double dummy contracts.

1. People can argue about whether double dummy solvers are accurate
2. People can argue about whether tricks taken is a good way to measure HCPs

Note: I don't disagree with your conclusions, but this isn't a very effective way to support them.
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#8 User is offline   pilowsky 

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Posted 2020-August-01, 04:25

View Posthrothgar, on 2020-August-01, 03:38, said:

But you haven't

You sample size is grossly insufficient and a bunch of the claims that you are making distract from your main point.

For example, if you want to show that HCPs are balanced, show the distribution of HCPs.
Don't use the number of tricks taken in double dummy contracts.

1. People can argue about whether double-dummy solvers are accurate
2. People can argue about whether tricks taken is a good way to measure HCPs

Note: I don't disagree with your conclusions, but this isn't a very effective way to support them.


Dear Editor -
Thank you for your comments - I've been waiting for my whole career to able to write this response. You are an imbecile. You clearly know nothing about sampling or statistics. I have used at least double the sample size needed as per the Nyquist theorem.
Do you have the vaguest idea what you are talking about, or do you just make this stuff up as you go along? Just asking.
1. The robots were given random hands to play and random results were collected. They are not double-dummy. There is only one dummy in this conversation.
2. Argue till you you are blue in the face. In fact purple with rage. I don't care. The result is the important thing, not the tricks. It is the 'barometer' as Bridge players like to mangle the language.

To address the question of better players sitting EW. Further experiments were undertaken. This time deals from the Vugraph archive were randomly chosen by BBO (perhaps the computer wants to make a point?).
The results are the same. By the way, Bob Hamman a notoriously weak player sat South in one of the games.
Posted Image
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#9 User is offline   shyams 

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Posted 2020-August-01, 04:37

ROFL. This is .... (I'm speechless).

What a moron!
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#10 User is offline   smerriman 

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Posted 2020-August-01, 04:49

Suppose the deals were biased and South was dealt 13 spades every hand. N/S would get 0 IMPs every hand. So that proves the deals are generated at random, right?
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#11 User is offline   pilowsky 

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Posted 2020-August-01, 04:58

View Postsmerriman, on 2020-August-01, 04:49, said:

Suppose the deals were biased and South was dealt 13 spades every hand. N/S would get 0 IMPs every hand. So that proves the deals are generated at random, right?


I paid for advanced robots.I set up a table. I put a robot on every seat. They all started playing with each other! After 12 boards I collected the data and started again.
It is all random.
What do Spades have to do with it? https://www.youtube....h?v=oGpFcHTxjZs


non est deus ex machina; även maskiner behöver lite kärlek; Wanneer elk gezegend ding dat u vasthoudt is gemaakt van zilver of van goud, verlangt u naar eenvoudig tin; Lätt som en plätt; uczciwość jest jedyną wartością
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#12 User is online   Vampyr 

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Posted 2020-August-01, 05:07

View Postpaulg, on 2020-August-01, 03:10, said:

Some club members have told me that they prefer South because it looks more natural to have North at the top of the screen, West on the left and East on the right. This seems more true when they first start playing on BBO.

At my club in real-life, the stronger pairs sit North-South through preference since they control the boards and the Bridgemates and don't trust the weaker players to do so. It may mean that they are less likely to win (for the reasons outlined by Adam) but this seems less important!

This element of control for N/S probably transfers subconsciously from real life to BBO, even though it does not exist.



How do the stronger pairs get the North-South seats? Is there some system besides first come first served?
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#13 User is offline   smerriman 

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Posted 2020-August-01, 05:30

View Postpilowsky, on 2020-August-01, 04:58, said:

I paid for advanced robots.I set up a table. I put a robot on every seat. They all started playing with each other! After 12 boards I collected the data and started again.
It is all random.
What do Spades have to do with it? https://www.youtube....h?v=oGpFcHTxjZs

The number of IMPs each side get is completely unrelated to whether dealing is biased or not. You stated that the end average being 0 means there is no bias, but that's 100% false - it would also be 0 if there *was* bias, like in my example.
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#14 User is offline   paulg 

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Posted 2020-August-01, 05:59

View PostVampyr, on 2020-August-01, 05:07, said:

How do the stronger pairs get the North-South seats? Is there some system besides first come first served?

It was first come, first served but traditionally certain places were left for particular pairs because they'd be upset if they had to sit elsewhere. It was, and is, an accommodating friendly club.

Now we toss for direction on most nights or draw for position in sim pairs.
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I don't work for BBO and any advice is based on my BBO experience over the decades
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#15 User is offline   hrothgar 

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Posted 2020-August-01, 06:10

View Postpilowsky, on 2020-August-01, 04:25, said:

Dear Editor -
Thank you for your comments - I've been waiting for my whole career to able to write this response. You are an imbecile. You clearly know nothing about sampling or statistics. I have used at least double the sample size needed as per the Nyquist theorem.
Do you have the vaguest idea what you are talking about, or do you just make this stuff up as you go along? Just asking.


Listen shiite for brains, I know that you're a short timer, don't know anyone on the forums, and seems to have some need to go and swing your dick around, so here's a bit of background information

I have multiple graduate degrees in this stuff including two from MIT.
(I graduated from there with almost a 5.0 average)

The job that I held before this one was the product manager for MATLAB's statistics system.
The job that I currently hold is Principle Data Scientist at Akamai

As for your "contributions" to this thread.

The Nyquist–Shannon sampling theorem comes out of signal processing. It describes the relationship between the frequency of a signal and the sample rate. It doesn't get used to determine the sample size for observational studies. It doesn't get used for classical power calculations.

> The robots were given random hands to play and random
> results were collected. They are not double-dummy.
> There is only one dummy in this conversation.

I agree.
It is the person who doesn't know that GIB uses double dummy solvers to determine its line of play
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#16 User is offline   pilowsky 

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Posted 2020-August-01, 06:17

View Postsmerriman, on 2020-August-01, 05:30, said:

The number of IMPs each side get is completely unrelated to whether dealing is biased or not. You stated that the end average being 0 means there is no bias, but that's 100% false - it would also be 0 if there *was* bias, like in my example.


Incorrect. The number of IMPS is the only important thing. The scoreline is what matters; in the end, nothing else matters - that is what points schmoints means. That is why it's an interesting game.

Also, your use of the adverb 'completely' is ludicrously and ridiculously unscientific and will not be permitted. Two pairs of robots each alike in dignity play the same 6 sets of 12 boards.
In the end, NS achieves the same aggregate result as EW.
Therefore, there is no bias in the way that the hands are dealt. quod erat demonstrandum.
As to the question of whether or not stronger players prefer to sit EW, If this were true then there would be a bias in the outcome compared with the results as compared with that achieved by top players in Vugraph competitions.
There was not so there isn't.
It is basically the same experiment that Francis Galton did to prove that prayer does not work. The royal family does not live longer on average than other people, yet people are praying for them all the time. "God save the King" etc. Of course, I never meant it when I said it. I was probably not alone.



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#17 User is offline   hrothgar 

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Posted 2020-August-01, 06:42

Note what happened when you repeated your little experiment
(I had to tweak the repeated 12.5 value because a ks.test doesn't like ties in a continuous distribution)
At a 10% significance level, a lot of your distributions are looking mighty different from one another

(Recall my earlier point about your sample sizes being grossly insufficient?)

> foo <- c(21.5, 24.5, 18.5, 32.5, 4.5, 10)
> bar <- c(12.5, 8, 18, 43.5, 31, 55)
> foo1 <- c(20.3, 23.3, 12.5001, 9.3, 1.2, 19.1)
> bar1 <- c(14.8, 6.8, 21.8, 32.4, 12.50001, 4.8)

> ks.test(foo, bar)


Two-sample Kolmogorov-Smirnov test

data: foo and bar
D = 0.33333, p-value = 0.9307
alternative hypothesis: two-sided

> ks.test(foo, bar1)

Two-sample Kolmogorov-Smirnov test

data: foo and bar1
D = 0.33333, p-value = 0.9307
alternative hypothesis: two-sided

> ks.test(foo1, bar)

Two-sample Kolmogorov-Smirnov test

data: foo1 and bar
D = 0.5, p-value = 0.474
alternative hypothesis: two-sided

> ks.test(foo1, bar1)

Two-sample Kolmogorov-Smirnov test

data: foo1 and bar1
D = 0.16667, p-value = 1
alternative hypothesis: two-sided

> ks.test(bar,bar1)

Two-sample Kolmogorov-Smirnov test

data: bar and bar1
D = 0.33333, p-value = 0.9307
alternative hypothesis: two-sided

> ks.test(foo,foo1)

Two-sample Kolmogorov-Smirnov test

data: foo and foo1
D = 0.33333, p-value = 0.9307
alternative hypothesis: two-sided
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#18 User is offline   hrothgar 

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Posted 2020-August-01, 07:29

View Postpilowsky, on 2020-August-01, 06:17, said:


As to the question of whether or not stronger players prefer to sit EW, If this were true then there would be a bias in the outcome compared with the results as compared with that achieved by top players in Vugraph competitions.
There was not so there isn't.



foo <- c(21.5, 24.5, 18.5, 32.5, 4.5, 10)
bar <- c(12.5, 8, 18, 43.5, 31, 55)

mean(foo)
sd(foo)
mean(bar)
sd(bar)
ks.test(foo, bar)

> mean(foo)
[1] 18.58333
> sd(foo)
[1] 10.09166
> mean(bar)
[1] 28
> sd(bar)
[1] 18.53915

Two-sample Kolmogorov-Smirnov test

data: foo and bar
D = 0.33333, p-value = 0.9307
alternative hypothesis: two-sided
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#19 User is offline   hrothgar 

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Posted 2020-August-01, 09:34

View PostVampyr, on 2020-August-01, 05:07, said:

How do the stronger pairs get the North-South seats? Is there some system besides first come first served?


I suspect that the proposed dynamic is that

Players who serve tables are more likely to be established pairs AND
Players who serve tables are more likely to sit N/S
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#20 User is offline   hrothgar 

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Posted 2020-August-01, 09:38

View Postsmerriman, on 2020-August-01, 05:30, said:

The number of IMPs each side get is completely unrelated to whether dealing is biased or not. You stated that the end average being 0 means there is no bias, but that's 100% false - it would also be 0 if there *was* bias, like in my example.


He's also using a peculiar amount of abstraction

Initially he is averaging together board results into six sets of 12 boards
And then he is calculating whether wins more IMPs and codes this as a -1 or a +1
And then he is summing across the number of boards

One wonders what would have happened had he chosen and odd number of hands.
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