Sources of variance in Bridge

[thepossum]

Hi

 

I was debating which forum to post this but it goes beyond robot Bridge and I know there are at least a few people who have analysed or are interested in this kind of thing.

 

From my experience the biggest contribution to my variance in results is either the field or the nature of the hands that may have been setup to be easier or harder to play, rather than being randomly generated

 

Anyone else have thoughts on the main sources of variance in duplicate Bridge. It appears clear from my results what it is

 

I forgot that it includes your partner - but in the case of Robot Bridge that source has been removed

 

While on the subject, despite apparent denials from some quarters would you not want to set up interesting advanced hands for the Bermuda Bowl against say a lesser tourney

 

EDIT. Nearly forgot. Which aspect of the game is most important in that variance

 

P

[AL78]

My thoughts:

 

1. Strength and variance in standard of the field. If you get the flat boards against the weak players and the technical BridgeMaster level 4 style hands against the strongest pairs, you will find it much more difficult to get a good score at the end.

 

2. Wrong pair wrong time or vice versa. Somewhat related to 1. above. You get the pair of beginners who don't play reverses and finish in the only making partscore their way that is impossible to reach by the other pairs, BOTTOM. You get the only pair that bids the cold slam against you, BOTTOM. The opposition overbid to a game going off on a trivial defence, TOP. You make an overtrick because the opponents carved the defence, TOP.

 

3. Hands that work/don't work with your system. You are playing strong NT in a field playing weak NT. You can end up rightsiding or wrongsiding NT contracts giving you a top or a bottom. Playing a strong NT, you have to open 1m on weak NT hands allowing LHO in with a 1M overcall which they couldn't do if you opened a weak NT. They therefore find their major suit part score for a top whilst everyone else goes peacefully one down in 1NT.

 

4. If you are directing and get called in the middle of a hand, you can lose focus which might be costly if it was a difficult hand.

 

5. The erratic players/gamblers who punt games which make on a lucky layout or throw poor hyper-aggressive overcalls at you which disrupt your bidding but you cannot punish them, which doesn't happen at the other tables.

 

6. Hand biases. You play 24 boards and declare twice, defend 18 times. Defence is harder that declaring and having to concentrate on nearly every board takes its toll, especially if you have had an early start and a full days work before playing in the evening. It also means when you are going pass pass pass follow suit follow suit much of the time because you keep picking up flat single digit point counts you are more reliant on exploiting the opponent's mistakes than generating good results from solid declarer play.

 

7. Best play sometimes fails and bad plays sometimes work on a particular layout. You have a 10 card trump fit missing the queen and the ace and king are in seperate hands. You cash the wrong honor first when they are 3-0, other people don't. You are in a 9 card fit after RHO opened with a pre-empt and you have to pick up the queen. You decide to play LHO for the queen on the principle of vacant spaces and finesse the second round into RHO's Qx. Other declarers blindly follow eight ever nine never and make one more trick than you. Bridge is a probabilistic game and the best you can do is take a line that is most likely to work best, not the line that is guaranteed to work on every deal.

 

8. Human error. doesn't matter how much is going your way if you or partner forgets a critical part of the system at the wrong time, or partner didn't give you a ruff because they lost concentration, or you butchered the defence or declarer play because you weren't concentrating/missed some critical information/opponents are erratic and don't have the hand they held in the auction.

 

Related to your last point, we had a situation last year in a competition where a beginner/improver plays with an experienced player and the trophy is awarded to the winning beginner/improver. What happened was there was a big bias in the hands (despite random dealing) which resulted in the experienced players declaring nearly all the time (I think one beginner claimed they declared twice in 24 boards or something like that). This was somewhat disillusioning for the beginners, and it prompted a discussion at the competitions sub-committee meeting that in future, anyone dealing boards for that competition should check the deal and reject large biases that put the cards one way or another i.e. the hands should be equable.

[pescetom]

Related to your last point, we had a situation last year in a competition where a beginner/improver plays with an experienced player and the trophy is awarded to the winning beginner/improver. What happened was there was a big bias in the hands (despite random dealing) which resulted in the experienced players declaring nearly all the time (I think one beginner claimed they declared twice in 24 boards or something like that). This was somewhat disillusioning for the beginners, and it prompted a discussion at the competitions sub-committee meeting that in future, anyone dealing boards for that competition should check the deal and reject large biases that put the cards one way or another i.e. the hands should be equable.

 

I trust you aren't transmitting your own hangup about unlucky days of random dealt hands to your beginners :)

More seriously, they have to learn to live with the sequence of hands as rub of the green.

 

It also looks to me as if the threat of high variance is more in the format of the competition than anything else. The variable of skill of the experienced player and (even more so, his ability to understand/predict/protect his beginner partner) will introduce a ton of variance, particularly if the partnerships are not randomly assigned (some partnerships will know each other, and the better experienced players may gravitate towards the better beginners). Also some beginners might not notice (or admit) that one or both members of the partnership is/are striving for the experienced player to become declarer, in order to do better in the competition. A more significant alternative format might be online with a robot partner, or an individual with separate classification for the beginners.

[AL78]

I trust you aren't transmitting your own hangup about unlucky days of random dealt hands to your beginners :)

More seriously, they have to learn to live with the sequence of hands as rub of the green.

 

It also looks to me as if the threat of high variance is more in the format of the competition than anything else. The variable of skill of the experienced player and (even more so, his ability to understand/predict/protect his beginner partner) will introduce a ton of variance, particularly if the partnerships are not randomly assigned (some partnerships will know each other, and the better experienced players may gravitate towards the better beginners). Also some beginners might not notice (or admit) that one or both members of the partnership is/are striving for the experienced player to become declarer, in order to do better in the competition. A more significant alternative format might be online with a robot partner, or an individual with separate classification for the beginners.

 

The objective of the competition is to give the inexperienced players a go with an experienced partner and learn something, for example if the inexperienced player misbids or misplays and the experienced partner can give advice/explanation. That can't happen very effectively if the inexperienced player is picking up so much dross they spend most of the evening passing and following suit and the experienced player gets most of the decisions, and the objective of the competition gets called into question.

 

In my case I still think I'm generating my own bad luck much of the time and people on here are being kind to me when I post a hand of woe, so my hangups are about my performance with what I get dealt as much as what I get dealt.

[pescetom]

The objective of the competition is to give the inexperienced players a go with an experienced partner and learn something, for example if the inexperienced player misbids or misplays and the experienced partner can give advice/explanation. That can't happen very effectively if the inexperienced player is picking up so much dross they spend most of the evening passing and following suit and the experienced player gets most of the decisions, and the objective of the competition gets called into question.

FWIW I don't think it should be necessary to invent a (rare) event to give the beginners a go with an experienced partner. I have always insisted (even when I was a beginner) that beginners should have the chance once a week to play with an experienced partner/mentor (this was the reason I signed up with a real bridge club in the first place, I had already grasped that books and internet were a better resource to learn theory). I have had varying success.

Initially it could only happen in a (very) competitive weekly simultaneous tournament: the experienced player tended to accept a beginner only as a last resort and then as revenge subject him to so much dross that he might well give up bridge altogether :(

Then it was conceded that an experienced player could play for free with a beginner, we created intermediate tournaments with less pressure and also as TD I stepped down on the dross: things got much better :)

Since lockdowns they lowered entry fees and eliminated prizes, but also eliminated free play with a beginner: it has become harder to find experienced volunteers and while I still offer myself with conviction, I do resent paying for the tournament when my only objective is to help partner learn and enjoy. I do my best to respect partner's bidding/play even when it is obvious that he has lost it, which I firmly believe is the right line even though it will never win the competition and will even cost trust from less perspicacious beginners ("hey, I did much better with others, how come?").

[mikeh]

I remember when computer dealt hands became common (yes, I’m old). Many players, especially the non-experts (and I was definitely a non-expert but didn’t fall into this camp) were convinced that the hands were vetted. Boring hands thrown out and freak hands allowed to stay.

 

Of course, what was happening was that hand dealt boards tend to be slightly non-random due to the variability of shuffling techniques. Thus when truly random hands (or as close to random as a good computer programme can generate) appear to be wilder…because they are. While we all know (or should know) the basic suit break percentages…the missing cards wh3n we have an eight card fit will be 3-2 68.5% of the time, a priori, I suspect that in hand dealt play it may be over 70% in a field where the shuffling is, at some tables, cursory. And so on.

 

I’ve played in a lot of events, including two Bermuda Bowls and several other WC events. Not for one moment have I ever thought nor wanted any vetting of the boards

 

Firstly, it’s extremely rare to see a pass out. Lots of players open almost all 11 counts even in first chair and few pass with any excuse in third if not vulnerable. Preempts are made on shorter suits than ever, and weaker hands.

 

Partscores are important. Making 2D on skilled play when 2D fails at the other table may be worth 5 imps

 

Secondly, if the field were persuaded that the boards are vetted, players will distort their bidding or play. They will suspect that bad breaks will be more likely than should be the case, or that unusual action is expected, and so on.

 

As for variance, I think it depends on the standard of play…the strength of the field. I’ve played a bit on BBO and, when dummy, occasionally look to see why we won ir lost a surprising number of imps. What I invariably find is that there are tables where the bidding was ridiculous and/or the play pathetic. The reality is that most bridge players have no idea how bad they are…and it’s their lack of skill that leads to silly results

 

I’ve played a lot of Regionals. These days one can play nothing but imps all week, which I deplore as a give-away to pros and their clients. But back in the day we had lots of pair games.

 

In my experience, playing in a Flight A pairs game, with lower flights not in the same field, if one scored 60% over two sessions, one had a chance of winning. Play in a stratified, and you’d better average 65% or better to be favoured to win. Why? Because in the Flight A, there is a higher and more consistent, across the field, calibre of play than in the stratified.

 

As for which aspect of the game is most responsible for variance…that’s been discussed ad nauseam over the years. I think there’s some consensus that at the expert level, it’s the bidding. All experts, by definition, can play the great majority of hands well….the number of hands on which a Michael Rosenberg will outplay me is significant in a long head to head match but over a short match or in a large matchpoint field, not likely to be decisive. But there are many, many different bidding methods in use. While many NA pro pairs play Meckwell Lite and may have common approaches to many auctions, most expert pairs play very finely tuned and idiosyncratic methods such that inevitably pairs will reach different contracts or play the same contract from different hands

 

Say you play 14-16 1N and at the other table they play 15-17.

 

Responder holds a decent 8 count. He’ll probably pass a 14-16 and probably invite a 15-17. So when opener has 16, the 15-17 pair may reach game or at least 2N, while the other pair rests in 1N. A swing is almost assured, yet neither pair did anything wrong.

 

In contrast, weaker players not only bid more randomly but are also more likely to screw up the play….surprisingly often saved by equally inept defence.

[thepossum]

Hi Mike

 

I wasn't saying that hands were vetted. With computer generated hands they are all designed in some way :) That was just an aside. Sorry if I offended any top players :) Maybe the elite players can make any hand look exciting and interesting

 

 

I was thinking in my case (mostly robot Bridge) its a combination of the quality/experience of the field, more bidding than play, and also any possible differences in how hands may be generated for different tourneys :)

 

Surely there are ways of scripting hand generation to have "easy" hands and "hard" ones - maybe we can have a couple of contract options and an over trick for the more advanced players :)

[PeterAlan]

With computer generated hands they are all designed in some way

No, they're not (in any meaningful bridge sense).

 

There are just less than 2^96 different bridge hands. What the computer does is to 'choose', essentially randomly, one hand after another from this sample space, and there is no more 'design' than that.

[thepossum]

No, they're not (in any meaningful bridge sense).

 

There are just less than 2^96 different bridge hands. What the computer does is to 'choose', essentially randomly, one hand after another from this sample space, and there is no more 'design' than that.

 

Yes they are. They have a script

 

Are you really trying to tell me they are all 100% parameterless generated hands. What about all the boring hands which make up the majority of Bridge hands I believe

 

Top tournament all the top elite players and teams sitting around, boring hand after boring hand - that's real Bridge - desperate for fun hands with some features :)

 

I appreciate all this stuff is highly secret and secure stuff. But I imagined top hand consultants or designers - let's be less technical and call them sculptors or artists - that's one my pieces over there currently played by USA 1. Like championship golf course designers

 

I just find it hard to believe that most script writers or hand designers make no attempt to add some features of interest to tournament hands

 

I couldn't estimate the figures. Maybe Mr Pavlicek's site has some figures along those lines but I imagine the Bridge hand universe rather like our mostly empty galaxy filled with little bits of sparkling interest from time to time

 

Also in line with Andrew's regular concerns over unfair sets of hands - you can't have that in a big match. Oh you were just unlucky this year. Can you imagine if the whole of the World Teams fell into a huge hole full of millions of featureless hands - infinity is big and you never know where you may end up with purely "random" hands. There may only be 2^96 to choose from but in fact for each of us there is an infinity. Imagine to be one of the unlucky ones who never saw or played an interesting hand because of their little part of infinity

 

I do appreciate the truth will never be known. Just endless speculation and debate. And of course they have infinity on their side as a defence

 

This is partly off topic of course - but has some relevance to the thread subject :)

[thepossum]

Can we return to the main topic please :)

[PeterAlan]

Can we return to the main topic please :)

What's the point of anyone spending their time trying to do so, if any response that doesn't comport with your preconceptions is going to be met with a delusional dismissal?

 

I, for one, have no intention of wasting my time on you again.

[thepossum]

If you miss the educated informed intelligent points I made and can only resort to ad hom then there is no point talking to you ever again

 

Don't be silly

 

The thread was about sources of variance in Bridge, not how hands are generated.

 

Seriously if you can't understand my post what is the point of disucssing anything

 

I addressed everything you and everyone else has said in this thread so far

 

Always someone with the attitude though :(

 

One of the points I made was that there is no way to test what you or I say anyway

 

The universe of Bridge Hands (in the real - not set theory sense) is an infinity. Not restricted by whatever number there are of different hands

 

Do they not also have to be "designed" for many tourneys to avoid perceptions of bias :)

 

Apparently also your idea of discussion requires my agreement with what you say :)

 

Here are a couple of questions for you

1. How many hands out of the N you describe would be regarded as interesting vs boring for top teams competition - has anyone ever worked it out

2. Is there not an infinite universe of Bridge Hands - possibly even an infinity of infinities etc depending how you conceptualise it?

3. How many hands does any individual get to see in their lifetime, out of that infinity

4. Is it possible to infer very much statistically at all in Bridge

5. Are we quibbling over the use of the word designed" Is the word engineered preferable or parameterised

6. Maybe the use of the word all rather than some or many - an infinity of deigned one and an infinity that are not designed. That's two infinities for starters

etc

 

But as I said if you want to debate this issue can we please do it in another thread and get back to the topic. The other aspects of the question are what I was getting at and interested in discussing

 

But to avoid further argument on your point I accept your approximate number of unique arrangements of cards which can be enumerated and written down in a nice simple expression like 52!/various other factorials

 

I am now going to play another 12 designed hands rather than arguing - thats 12 out of the infinity of one specific format of GiB ACBL tourneys :)

[smerriman]

One of the points I made was that there is no way to test what you or I say anyway

Bridge dealers are subjected to extensive statistical analysis to ensure the hands line up with all measures of randomness. There are many people who have put forward conspiracy theories about the one BBO uses being biased, and every single time they've been proven wrong by statistics. Ones used for higher level competitions are even more strictly tested.

 

That's aside from the fact that biasing them based on 'difficulty' is extremely difficult to program in the first place, and simply not worth the effort.

[thepossum]

Having just played one set of 12 in a tourney type that I have played many times, with an average well above my average across other tourneys, my poor performance today suggests, possibly, that emotional state impacts seriously on Bridge ability. I only have a few such cases, maybe not enough to draw any inference. It does appear a repeated pattern

 

So I imagine psychology plays an important part in major tourneys. With all respect due to said players and teams

 

Doesn't take much to psych me 😔

[mikeh]

I am one of the few regular posters who can claim, with justification, to have played quite a lot of ‘elite’ level bridge. I’m not quite good enough to actually do well at that level, though my teams have done things such as beat Lavazza in a short match, almost beat the current world champions in November, losing by 9 imps over 60 boards, and so on. Thus, while I’m not an elite player, I do know what it’s like to play elite-level bridge against world champions…not just in November but for many years.

 

I say this only so that I can assure you, and any interested readers, that you have no idea…none at all..about elite bridge.

 

Boring hands? There are never…never…any boring hands in world class competition, in important events. A pass out might be ‘boring’ but it may well have been opened at the other table and you don’t know until the comparison. Let me be clear….a hand may appear boring on vugraph, where we see all 52 cards and (usually) can see the outcome. The players don’t have that knowledge.

 

Maybe a balanced 16 opposite a balanced 12 count…1N 3N….boring?

 

Well, opening leader is often going to be thinking about the lead. Declarer wants to assure 9 tricks but also play, if possible, for ten or eleven. The defence may quickly realize they can’t set the hand, but that doesn’t make it boring!

 

Each player, other than dummy, is going to be thinking very, very hard, trick by trick.

 

You remind me of those opponents I sometimes play in low level events…say a Regional Swiss in the early rounds

 

I’m not a fast player…I used to be, then I learned (from a very good player) to slow down…and to THINK.

 

So…the hand looks easy…almost boring. But….what if the cards lie in an unfriendly fashion? What if the defence does such and such? Is there anyway to guard against that? Could LHO be strip squeezed if that’s what’s going on?

 

Yes, I almost certainly have nine tricks…but can I get ten without jeopardizing 3N?

 

Etc, etc.

 

Then an opponent will complain about my being slow. ‘Come on, play faster’

 

My standard response is along the lines of: sorry, I was thinking. Now you’ve interrupted me, I have to start all over again

 

Actually, I rarely say it…any player who doesn’t know why I’m thinking won’t understand anyway.

 

I’ve never won nor lost an important match by just one imp, but I know players who have and I’ve definitely won and lost by two or three. When it’s a knockout match, unless it’s turned into a blowout, every hand demands intense concentration, which is why fatigue is such an important factor in long multi-day events. And in round robin events or stages, one can’t let up just because it’s clear that one side is beating up their opponents…the use of victory points makes every trick important. I once failed to qualify for the KO stage of our team trials by less than 1VP.

 

Now, having said that, sometimes…rarely but sometimes….a hand will appear to be routine. We’re in 3N, they cash four tricks and we claim…nothing to it. But every player is hyper-focused during the auction, and the play doesn’t take long because declarer will claim very quickly…and the respite lasts until one pulls out the hand for the next board. Trust me, nobody EVER gets bored playing elite bridge.

 

Terence Reese once wrote, and I paraphrase, that if a ‘dub’ (then, in a England, a term for a duffer or mediocre player) could listen in on what an expert is thinking during a hand, he wouldn’t believe it.

 

I think that describes you perfectly. Only a ‘dub’ would imagine that playing high level bridge against world class opponents with world class (or, in my case, almost world class) partners and teammates could ever be ‘boring’.

[PeterAlan]

For those that might be interested, I would mention Law 6 (especially parts A, B, D2 & E4) which essentially requires that the deals in each event be random "unless the purpose of the tournament is the replay of past deals".

 

And apropos 'boring' deals, over the years partner and I have played a dozen or so matchpoint deals against Zia at various EBU events in London. We have, memorably, one outright top amongst those deals: partner, dealer, inadvertently passed a balanced 14-count and the deal was passed out. Neither Zia (second in hand) nor his partner had an opening bid, but if they had got into the auction 4 spades was on their way.

[pescetom]

Even at I/A level, I find passed out hands almost always interesting. I am surprised when fellow competitors complain that such nonsense should be suppressed during tournament creation, particularly as more often than not the same player had a reasonable opening bid.

[AL78]

For those that might be interested, I would mention Law 6 (especially parts A, B, D2 & E4) which essentially requires that the deals in each event be random "unless the purpose of the tournament is the replay of past deals".

 

And apropos 'boring' deals, over the years partner and I have played a dozen or so matchpoint deals against Zia at various EBU events in London. We have, memorably, one outright top amongst those deals: partner, dealer, inadvertently passed a balanced 14-count and the deal was passed out. Neither Zia (second in hand) nor his partner had an opening bid, but if they had got into the auction 4 spades was on their way.

 

I wouldn't call hands like that "interesting", I just find it irritating to be punished for an opponent's blunder (it's bad enough being punished for my own blunders). Unlike many at my club I don't find hands that have high distribution interesting just because they have high distribution and it is a guessing game how high to bid and an element of luck who you are against. I find hands interesting that have an instructive element about them, such as deducing a winning line through subtle inferences I didn't pick up at the time, or where more sophisticated defensive signals would have guided me to the killing defence.

[PeterAlan]

I wouldn't call hands like that "interesting", I just find it irritating to be punished for an opponent's blunder (it's bad enough being punished for my own blunders). Unlike many at my club I don't find hands that have high distribution interesting just because they have high distribution and it is a guessing game how high to bid and an element of luck who you are against. I find hands interesting that have an instructive element about them, such as deducing a winning line through subtle inferences I didn't pick up at the time, or where more sophisticated defensive signals would have guided me to the killing defence.

I was careful to say the hand was 'memorable' for us, and Zia wasn't put out - the previous 6 deals had been good for them, and he could see the curiosity. Whilst I meant the tale primarily as an anecdote the hand itself was actually intrinsically quite interesting too, but I take your point.

[AL78]

I say this only so that I can assure you, and any interested readers, that you have no idea…none at all..about elite bridge.

 

Boring hands? There are never…never…any boring hands in world class competition, in important events. A pass out might be ‘boring’ but it may well have been opened at the other table and you don’t know until the comparison. Let me be clear….a hand may appear boring on vugraph, where we see all 52 cards and (usually) can see the outcome. The players don’t have that knowledge.

 

Maybe a balanced 16 opposite a balanced 12 count…1N 3N….boring?

 

I'm only accustomed to playing low to mediocre quality club bridge and I agree that hands that look boring from the auction are often not during the play. At MPs you have to work out what is going on and concentrate throughout to avoid blowing a trick through a lead into a tenace or a careless discard setting up a suit in declarer's hand. I have got better at that over the years but there do exist hands which I class as boring. The classic example is at the end of the second round having defended on five of the first six boards, the opponents bid to 3NT which is the fourth game their way, I think about the lead having worked out partner's strength and when dummy comes down am glad I found a decent or even the best lead. Declarer proceeds to cash 10 tricks off the top and we get a bad score because two of the other five pairs didn't bother bidding it. After a couple more of those types of hands I start to wonder why I bothered to turn up (then I remember it is for the pleasure of my partner's company not the quality of the bridge).

[hrothgar]

 

I do appreciate the truth will never be known. Just endless speculation and debate.

And of course they have infinity on their side as a defence

 

 

This is simply not true.

 

The WBF adopted a program and an associated process for generating deals for its tournaments to forestall just this sort of discussion.

 

The system is called Square Deal.

It was developed by Hans Van Stavern.

 

It encompasses

 

1. An open source program to generate deals

2. A method of selecting seeds for hand generation

3. A process by which tournament organizers can pre-commit to using a salted version of a specific seed in advance of the tournament proper

4. A process to select the salt for the seed using public sources at the time of the event

5. Methods to validate that hands for the tournament were generated from the seed in question.

 

These types of methods are very common in fields like cryptography which often has to deal with very similar types of problems.

 

Applying them to bridge is not difficult

[hrothgar]

 

One of the points I made was that there is no way to test what you or I say anyway

 

 

Incorrect

[thepossum]

Incorrect

 

I disagree. Within my bounds of certainty anyway

 

Has anyone ever written a good paper on the subject - or book. I am looking for a good project despite not feeling qualified

 

It was very unlikely for this sequence of hands to be totally random - before I am jumped on - yes we can show p<.00001 that this set of hands had x different from that, or this was not different from that, or we didn't engineer things to make it look not different from that. If the Bridge universe is so big how small does p have to be?

 

or I have a mate who helps organise the World Teams

 

There must be a place in such a huge "universe/s" as bridge where any weird sequence of hands is possible

 

What even constitutes a hand. Surely it is more than just an arrangement of cards???

 

And while we are here what makes a hand interesting is a complex matter too ( I risk causing offence so will go not further on the matter)

 

In case I am ever accused of disrespect I value your knowledge and opinion on such matters very highly and am grateful for you joining the thread Richard

 

I just find it one of the most interesting conceptual problems I have ever considered and its well beyond me. The likes(????) of John Horton Conway and John Nash come to mind. As I say I could only dream. I reckon I know enough to know it goes beyond high school probability theory

 

I don't need anymore fights so will just accept everything anyone says on the matter

 

As you can see despite my love of simplicity you can see why so many projects I worked on got out of hand very quickly and caused me problems

[mycroft]

So, have you read the document that hrothgar pointed you to? (granted, because he typoed the name "SquareDeal", and "Square Deal" with a space means something different, it may have been difficult for you to do so.) The doc files, in particular the BigDeal simplified, the introductory parts of the BigDeal detailed and the SquareDeal documents, will give you the information you need.

 

Some choice quotes:

Before we can design new software it should be clear what it should achieve. Dealing software is supposed to simulate correct shuffling by the players themselves, and should deviate from this goal as little as possible. Therefore dealing software should conform to certain minimum requirements:

1. The software should be able to generate every possible bridge deal, since that is also possible with manual dealing

2. The software should generate every deal with the same probability, without being influenced by the board number, previous hands or any other circumstance

3. It should be impossible to predict deals, even after having seen all other deals in the session

 

To avoid all these flaws, the new software was designed according to a couple of principles:

1. Gather more than 96 bits of randomness to stand a chance of satisfying the requirement to be able to generate every possible bridge deal

2. Use a PRNG with good statistical properties to satisfy the requirement of generating all hands with equal probability

3. Use a PRNG with strong cryptographic properties to satisfy the requirement of not being able to predict deals

5. Make it as difficult as possible for the operator of the program to make the sort of mistake that would lead to a duplicated series of deals

 

The fifth principle will be taken to extremes: as far as possible the software should view the operator as an enemy in the struggle to generate unique sequences. Whatever the operator tries, he should not be able to get the program to generate the same sequence twice.

(my emphasis here. #4 is "allow multiple output formats to make the output easy to use". The software these two quotes reference has been available for use, and the source code available for review, and has been used for most tournaments worldwide, for over a decade)

 

And since there were issues with "potential manipulation of the output" brought up in the last 10 years, SquareDeal now:

 

SquareDeal ... uses the well-known program BigDeal for actual dealing, but adds two things:

1. An easy way to make multiple sets of deals for various sessions using consistent naming

2. A way for participants to check the hands were dealt honestly and without any tricks by the organizer

Using SquareDeal a specific procedure is needed, with various phases, by organizer and participants. There is no actual need for participants to do anything, but if they want to check the hands after the tournament, they need to do something even before the tournament.

Which involves "Using something I keep secret (until afterwards, for post-game checks), something I release publicly (so that I can't manipulate anything during dealing), and something that doesn't exist until well after I commit to the public information (but we can both find out trivially when it does happen)".

 

Don't just say "I can see all these problems, therefore there's no way to disprove my conclusion, therefore somebody must have done it." Yes, there are all those problems. People have been trying to come up with solutions to these problems (in and out of bridge) since Shannon's work in Bell Labs in 1943. There are (complicated) solutions to a lot of the trivial problems, at least.

[hrothgar]

 

There must be a place in such a huge "universe/s" as bridge where any weird sequence of hands is possible

 

 

The following might be a helpful way to frame some of this

 

1. Start by enumerating every possible bridge hand in existence

2. Sort these hands however you want

3. Assign a unique number to each and every bridge hand

 

Next create a pseudo random number generator that is capable of creating a stream of numbers between one and the number of possible bridge hands

Seed the PRNG and then start walking though the database of hands until you have all the hands that you need for your event

 

It is absolutely possible for this type of technique to create some biased set of hands.

 

Imagine a world in which the way in which you sorted the set of bridge hands had some period to it. (All hands that correspond to a number than ends in a zero contain a singleton or something like that). And then, assume that the your stream of numbers is coming from a Linear Congruent Generator or some such where the number stream also has a period to it. And these two systems have the same frequency

 

Well, in this case the hands that you're generating would very likely be biased.

 

However, so long as you're living in a world in which the PRNG that you're using and the method that you used to assign numbers to hands didn't collide like this you're golden. (And, its possible to chose the sorting method and the design of the PRNG such that they shouldn't share this sort of ugly property)