[pooltuna]

EricK, on Apr 13 2010, 12:39 PM, said:

I remember a time when I played the J from QJ and the declarer "accused" me of being tricky!

Be delighted, be very delighted! This is a reputation you want your opps to have of your play as it increases their anti%age play.

[rwbarton]

Since I happen to have a sample of several million hands played on BBO handy, I thought I would do a study of how defenders play from QJ in real life. Of the first 66000 hands my program looked at where a defender held QJ tight, the defender played the Q first only 52% of the time. However, this includes situations such as the opening lead and when partner is leading the suit, and does not take into account the contract. Suggestions for better parameters for the study are welcome. I think I'll try only hands where QJ is in the trump suit next.

[jdonn]

rwbarton, on Apr 13 2010, 06:01 PM, said:

Since I happen to have a sample of several million hands played on BBO handy, I thought I would do a study of how defenders play from QJ in real life. Of the first 66000 hands my program looked at where a defender held QJ tight, the defender played the Q first only 52% of the time. However, this includes situations such as the opening lead and when partner is leading the suit, and does not take into account the contract. Suggestions for better parameters for the study are welcome. I think I'll try only hands where QJ is in the trump suit next.

Can you restrict to only times when the opponents lead the suit to that trick?

[cherdanno]

Truly bad players will always play the J. I think we are talking about "good" players here, i.e. players who are good enough to try to do something tricky.

Btw, I just wanted to mention that I am completely exploitable and always play the Q.

[helene_t]

cherdanno, on Apr 14 2010, 01:48 AM, said:

Truly bad players will always play the J. I think we are talking about "good" players here, i.e. players who are good enough to try to do something tricky.

Btw, I just wanted to mention that I am completely exploitable and always play the Q.

That's the optimal strategy if opps think you are a noob.

Then again, if opps think you think they think you are a noob, you should always play the jack

[eyhung]

I randomize by using a similar technique I learned from poker -- glancing at my digital watch and looking at the final seconds digit when I can anticipate a later decision (obviously not when i'm about to play.) Odd is one direction, even is another. I think this is unexploitable even if known, especially if I wear sunglasses.

[campboy]

That sounds illegal to me. Law 40C3a.

Quote

Unless permitted by the Regulating Authority a player is not entitled
during the auction and play periods to any aids to his memory,
calculation or technique.

[rwbarton]

jdonn, on Apr 13 2010, 07:10 PM, said:

rwbarton, on Apr 13 2010, 06:01 PM, said:

Since I happen to have a sample of several million hands played on BBO handy, I thought I would do a study of how defenders play from QJ in real life.  Of the first 66000 hands my program looked at where a defender held QJ tight, the defender played the Q first only 52% of the time.  However, this includes situations such as the opening lead and when partner is leading the suit, and does not take into account the contract.  Suggestions for better parameters for the study are welcome.  I think I'll try only hands where QJ is in the trump suit next.

Can you restrict to only times when the opponents lead the suit to that trick?

I ran the study using this rule, which I took to mean "consider instances where a defender held QJ in a suit, and the first of those cards was played following suit to declarer or dummy's lead", and I also eliminated cases where the defender was GIB.

Among my sample of BBO hands, there were more J plays than Q plays: 59.1% of the time the J was played (out of 74703 instances). I also grouped the instances by BBO username. For instance, among the 339 people who faced the problem exactly 6 times, there were

23 people who played the J 0 times (always the Q),
27 people who played the J 1 time,
51 people who played the J 2 times,
51 people who played the J 3 times,
49 people who played the J 4 times,
65 people who played the J 5 times,
74 people who played the J 6 times.

It's hard to make any solid conclusions from this data, but it looks like there are a lot of players who always play the J, some players who always play the Q, and some players who play randomly. (Again, this is from my utterly unscientific sample of hands played on BBO.)

[jdonn]

campboy, on Apr 14 2010, 05:55 AM, said:

That sounds illegal to me. Law 40C3a.

Quote

Unless permitted by the Regulating Authority a player is not entitled
during the auction and play periods to any aids to his memory,
calculation or technique.

What he is doing definitely doesn't aid "memory" or "calculation". I don't think it aids "technique" either though you could argue that one (to me that sounds more like having a book on your lap explaining compound squeezes). I think it just aids "strategy", which is not mentioned.

[cherdanno]

rwbarton, on Apr 14 2010, 10:26 AM, said:

I ran the study using this rule, which I took to mean "consider instances where a defender held QJ in a suit, and the first of those cards was played following suit to declarer or dummy's lead", and I also eliminated cases where the defender was GIB.

Among my sample of BBO hands, there were more J plays than Q plays: 59.1% of the time the J was played (out of 74703 instances). I also grouped the instances by BBO username. For instance, among the 339 people who faced the problem exactly 6 times, there were

23 people who played the J 0 times (always the Q),
27 people who played the J 1 time,
51 people who played the J 2 times,
51 people who played the J 3 times,
49 people who played the J 4 times,
65 people who played the J 5 times,
74 people who played the J 6 times.

Waiting for Helene to tell us how often we have to see someone play the Q from QJ until it is worth trying exploit his tendency.

[campboy]

jdonn, on Apr 14 2010, 04:53 PM, said:

campboy, on Apr 14 2010, 05:55 AM, said:

That sounds illegal to me. Law 40C3a.

Quote

Unless permitted by the Regulating Authority a player is not entitled
during the auction and play periods to any aids to his memory,
calculation or technique.

What he is doing definitely doesn't aid "memory" or "calculation". I don't think it aids "technique" either though you could argue that one (to me that sounds more like having a book on your lap explaining compound squeezes). I think it just aids "strategy", which is not mentioned.

"Strategy" would be whether or not to randomise; it doesn't aid that. It does aid his randomising technique, though, I would say.

[eyhung]

Anything in your external environment can aid your randomization technique if you look hard enough -- such as the last digit of the round timer, the number of objects on the table, or even the color of a random person's shirt. This is in contrast to a bridge book, system notes, or a calculator. The law is directed at specific aids, not general ones.

[Jlall]

You should often be giving suit preference rather than making a random play fwiw.

[Cascade]

eyhung, on Apr 15 2010, 06:21 AM, said:

Anything in your external environment can aid your randomization technique if you look hard enough -- such as the last digit of the round timer, the number of objects on the table, or even the color of a random person's shirt.  This is in contrast to a bridge book, system notes, or a calculator.  The law is directed at specific aids, not general ones.

Then there is improper use of the word "any" which gives the law a general meaning.

[jdonn]

Cascade, on Apr 14 2010, 02:48 PM, said:

eyhung, on Apr 15 2010, 06:21 AM, said:

Anything in your external environment can aid your randomization technique if you look hard enough -- such as the last digit of the round timer, the number of objects on the table, or even the color of a random person's shirt.  This is in contrast to a bridge book, system notes, or a calculator.  The law is directed at specific aids, not general ones.

Then there is improper use of the word "any" which gives the law a general meaning.

True, but a totally literal interpretation of "any" is not feasible. For example, vitamins I took that morning aid my memory (I am still digesting them during the auction and play period). A book I read 8 years ago aids my technique (it is still aiding my technique during the auction and play period). Etc.

[Echognome]

I think we just need to apply some sensibility here. If I use my watch or have a private rule* about how to use external information on the board, whether it be vulnerability or board number modulus N or whatever, I feel that is within the spirit of the laws. If I bring an electronic random number generator to the table, then I feel that is an aid to technique. I understand that I'm saying I think it's ok to use a watch as a randomization device, but not a separate standalone randomization device. I view the difference mainly from the point of view of enforceability perspective. It seems highly impractical to ban people from wearing watches or looking at their watches. Are we going to also ban people from looking at the board number or vulnerability or who is dealer? Any laws that are completely unenforceable are pointless. However, banning someone bringing a device to the table for the specific purpose of producing random numbers would seem against the spirit of the "aid to technique" part of the laws.

* I stress private rule, because I think it should be (is?) illegal to have an agreement with partner on your randomization rule, particularly if undisclosed and even if disclosed. For example, suppose partner and I both have a rule that if we have QJ tight, we play high on odd number boards and low on even number boards. My problem with having this rule, even if disclosed, is when would you disclose it? Would it require a pre-alert? You obvious cannot alert it while defending.

[Jlall]

You can randomize based on your cards also (like if I have the beer...)

[helene_t]

cherdanno, on Apr 14 2010, 05:16 PM, said:

rwbarton, on Apr 14 2010, 10:26 AM, said:

I ran the study using this rule, which I took to mean "consider instances where a defender held QJ in a suit, and the first of those cards was played following suit to declarer or dummy's lead", and I also eliminated cases where the defender was GIB.

Among my sample of BBO hands, there were more J plays than Q plays: 59.1% of the time the J was played (out of 74703 instances).  I also grouped the instances by BBO username.  For instance, among the 339 people who faced the problem exactly 6 times, there were

     23 people who played the J 0 times (always the Q),
     27 people who played the J 1 time,
     51 people who played the J 2 times,
     51 people who played the J 3 times,
     49 people who played the J 4 times,
     65 people who played the J 5 times,
     74 people who played the J 6 times.

Waiting for Helene to tell us how often we have to see someone play the Q from QJ until it is worth trying exploit his tendency.

Hmmm ... suppose he plays the queen from QJ with probability p. If we miss two spots and he would play the queen only from Q sec and QJ tight the the a priori the probability of QJ is 12/23 so the posterior is p*(12/23) / (p*(12/23)+11/23) which breaks even for p=11/12.

Suppose we model p as beta (1,1), then the posterior mean of p after having observed him playing the queen n times from QJ tight and never the jack from QJ tight is (n+1)/(n+2), so we have

(n+1)/(n+2) = 11/12

i.e.

n=10.

Here I have not made any attempt to model the data. beta(1.4,0.9) fits the data reasonably. That would give us, in 33900 players:
0 1 2 3 4 5 6
2301 3381 4213 4701 5650 6218 7436

For beta(1.4,0.9) the equation becomes
(n+1.4)/(n+2.3) = 11/12

so 9 is enough.

This is not quite correct since our decision depends on the posterior mean of p*(12/23) / (p*(12/23)+11/23) rather than the posterior mean of p but I don't think it makes much difference.

BTW last friday I gave a talk at a symposium on Bayesian methods in medical research. I talked about safety monotoring in drug combination studies. Suppose a patient takes both booze and coke so when he collapses due to a booze intoxication it is a slight indication that he is hypersensitive to booze only since otherwise he might have collapsed due to coke intoxication first. Now suppose we have, for a particular group of patients, evidence that if they afterwards appear to actually be hypersensitive to both drugs they will always collapse due to the booze intoxication and therefore being taken off study before they get to the point of being coke intoxicated, then the restricted choice argument weakens. Same thing.

[gwnn]

this is very interesting, I would have thought the graph would be a bit like a U, with a possible smaller peak at the middle! weird weird weird. but then again matmat says about BBO experts that they truly play their cards randomly.

Helene's reply was also interesting but only after extensive research on Bayesian statistics on wikipedia.