[Stephen Tu]

Good god you use a ton of words to say not much. I will try to edit it down to the core of the argument.

Povratnik, on 2018-December-18, 16:09, said:

You're trying to prove that trying to drop the West's king is clearly a better line than safety play, without EVER actually saying it. And you know what? Not only that you failed to convince me that your line is better; you didn't even convince me that it's your real opinion! I seriously tend to think that the main reason for your efforts is sheer inertia. How this chain of misunderstandings began?

Huh? I thought I already stated this many times, fairly clearly. This is my claim:trying to drop west's stiff K yields more matchpoints than taking the safety play in the long run, if >= 89% of the relevant field is in 4S.

Or in other words, "IF 89+% of the field is in 4S, you SHOULD play for the drop", but "if <89 % of the field is in 4s, the others being in contracts yielding plus scores < 620, you SHOULD play safe".
Clear enough for you? I really don't get your complaints about my clarity or "may vs.should". Most everyone else on the thread understands what I meant.

Quote

You and Cyberyeti sent me about the same message. In my words:
There are certain boards where you may risk the game having only a slight frequency advantage; such line can even bring some +EV. This board is one of them.
I answered to both, without expressing any disagreement. But you somehow misunderstood me and mistakenly said (error No 0) that my final statement wasn't correct. In the next post you've stiffly withdrawn this qualification, but continued to discuss as if I'm somewhere wrong. Not only you didn't say where do you thought I'm wrong, you haven't even pointed in the direction of my apparent wrongness. You're explaining general things - probabilities, mathematical expectation, mechanism of pair tournaments... I never asked, but I am asking you now - what made you to assume that I didn't know all that stuff you're writing about?

You basically claimed it's always right to take the safety play to make game if available on any board. A blanket statement, not restricting yourself to this particular board where the edges are small and thus a small number of outlier contracts should favor the safety play. That the field always has enough outlier contracts that the safety play is always right. You said if that if you score 620 when 650 and -100 are also possible that you will always score well above 50%. These just aren't true statements. Some fields are more homogeneous than others, and some boards are flatter than others. One has to be able to estimate how flat a board will be based on the board itself and knowledge of the field, to guess how many will be in the same contract. The more people are in the same contract, the more that favors eschewing safety plays even for very small edges. And if the edge is larger for the overtrick, then one needs less flatness to justify not playing safe. My general claim is don't play safe at matchpoints when in normal contracts. Only when edges are very small as here should one even consider playing safe, if you feel there are enough outlier contracts (> 11% on this board). Your initial posts read to most as "always play safe, making game always > 50%" which is just not true in my experience. This board is close because the edge is small, it's not clear if 90+% are going to be in game or only say 85%.

Quote

We weren't talking about "just being plus", we're talking about making a GOOD contract. In this particular case, 4s is the very best contract available to NS; 620 can't be bad and can be a great result (most of the time, it will be a VERY good result).

620 CAN BE BAD. If the K is stiff offside, and 90% of the field is bidding the contract and banging down the ace, you get a 10% score. Wouldn't you much rather have 55% making 5 like everyone else? Is a 10% score not bad?

Quote

- Specifically, if you watch that parameter alone (the number of pairs playing the same contract), overtricks value (if we're talking about the result) doesn't go UP, it goes DOWN. You're more than qualified to check that...

I don't get this argument at all. If a ton of people miss game, overtricks don't matter at all. You get a fantastic score for bidding and making game, and it's right to play safe. But if a ton of people are in the exact same game contract, the overtrick matters A LOT. If everyone is dropping the stiff K offside, you get a near bottom if you don't. The more people that are in the same contract, the more MP are swung by getting the overtrick or not. If people are in different contracts then the overtrick swing doesn't matter, the making vs. going down does.
You are just wrong here.

Quote

Let's assume that every NS pair played the same contract. As it's already said - you have frequency advantage, I have points advantage. In this case, my advantage is clean ZERO. So your frequency advantage, no matter how small, literally guarantees you +EV.

Huh? WTF frequency vs. points? Let's say there are 100 other pairs, all in 4s, all play for the drop. You win 100 MP when you are right, when LHO is void. You lose 100 MP when you are wrong, when LHO has stiff K. There is no "point advantage" when everyone is in the same contract. It's just pure frequencies.

There would be a point advantage if the scoring were total points or IMPs, because you only lose 50 pts/1 IMP when wrong but gain 600+/13+ when right. But at MP it's simply moving tie to loss either way, there's no "point advantage".
Your point advantage comes into play *when there are outlier contracts*. This is because now when you win, you swing a half matchpoint point against the overtrick players AND a matchpoint against outlier contracts, while the overtrick players don't gain anything extra against the outlier contracts when the overtrick was available. So thus the more outliers, the more that favors the safety play, and vice versa. *PROPORTION OF FIELD IN SAME CONTRACT IS WHAT MATTERS*. Proportion, not raw number.

Quote

nonsense about board-a-match teams vs pairs

Bunch of math arguing that I win a full board at board-a-match but only say half a board at pairs. This stuff is cancelled out by the same phenomenon in the other direction; when you beat me you gain full board at board-a-match but less at pairs. It's irrelevant.

My statement is that going for overtrick is right if >89% of the field is in game, absolute size of the field, whether 3 tables, 30, tables, 300 is basically irrelevant. Smaller field favors going safe because single outliers equate to a bigger chunk of the field; if one table in 8 is weird you want to play safe; if it's only one table in 13 then you don't.

Quote

Yes, everybody's gains or loses depend on percentage of the field in every contract that was played in the board. So what?

So what? So your strategy should change depending on your estimate of what percent of the field is in what contract.The correct answer is not to "always play safe" as your initial post appears to suggest.It is not to "never play safe" either.One has to estimate how much of the field is in the same contract, and compare the edge of the safety play vs. the overtrick play, and make your choice based on all the numbers.

Quote

The METHOD is deeply wrong. Save the few complete but limited examples that you gave us, you're trying to achieve something by analyzing our group in isolation. That's bound to failure. In this particular case, you're referring to size/percentage of our group (in the field) as if it's somehow possible to change it, without also changing the percentage of other groups. No wonder results are so erratic...

My method was fine. If the pair drops out of the same contract (favoring drop), it was assumed to drop into the relevant safety play group (I specifically excluded +800 group, out of reach). And I calculated the breakeven percentage. I just was sloppy with the algebra earlier and came up with a number smaller than reality the first time.

[Povratnik]

@Stephen Tu

Stephen, you are VERY quick on trigger! There is no way you could read and assimilate such a big post in an hour, yet you immediately wrote a fairly long "answer". The result is very disappointing...
Your post consists of 9 segments and virtually (literally?) each one has a flow. Most of them I can knock down without saying anything new, just by putting a quote from some of my previous posts...

Stephen Tu, on 2018-December-18, 18:26, said:

Good god you use a ton of words to say not much.

That's precisely my objection to most of your posts . Of course, since I am using foreign language, my posts could be even worse. But I wasn't much active on this forum so far; so you can check all my posts and convince yourself that my posts are usually short and to the point... Unless I am writing to YOU.
Generally, your posts are the hell of a mess. Specifically, when I am writing to you, I tend to fall in one and the same trap - I assume what are trying to say, instead of just asking you that. But my last post had to be that long, because I want to stop inefficient practice and correct procedural mistakes made by both of us. I wrote ALL that had to be written but, unfortunately, most of the content remained undigested by you. So we have a problem again...

Stephen Tu, on 2018-December-18, 18:26, said:

I will try to edit it down to the core of the argument.

Well, you missed it, I hope not deliberately... The core of the argument is my claim that you're looking at the wrong side of proportion. I explained it in the last part of my post. You ignored it totally.
A guide for reading my previous post:

Spoiler

My post consists of three parts.
In the first part, I am exposing my dissatisfaction with the very process of our discussion. You made a few comments of that part, but totally ignored my (I believe - legitimate) wishes. I'll return to that.
At the end of first part and beginning of second part, I said:

Povratnik said:

...
So I'll not try to determine whether any of your deep convictions are wrong (they probably aren't). I'll concentrate on positive story that I have to tell - how these things really operate...
...
In your two large posts, there are four parts that I painted red, because (very) wrong conclusions could be implied from them. I'll cross over them, not necessarily in chronological order.
Once again - whether you meant it wrongly, or were you just sloppy - isn't nearly as important, as positive story that I'm going to tell...
...

In the second part, I explained why the red paint (less important) and how these thing really operate (MUCH more important). And built the apparatus, so I can speak freely in the third part, which is THE GOAL of the second part.
But you dedicated majority of your post to petty mistakes and misunderstandings from second part, without dedicate ONE SINGLE WORD to the third part. As if you haven't read it at all...
I understand, you were exhausted because of the length of second part, but you REALLY SHOULD read the third part carefuly.
It's significantly clearer and shorter that your average post.

At the beginning of the post, I said:

Povratnik said:

OK, I'll give you what you're asking for, but I would really like to shorten yours and my further posts, so I'll try to crystallize the things on global level first. It's by far more important than petty mistakes.

I continued to explain the reasons of my dissatisfaction. See a few quotes:

Povratnik said:

...
You're trying to prove that trying to drop the West's king is clearly a better line than safety play, without EVER actually saying it.
...
You're explaining general things - probabilities, mathematical expectation, mechanism of pair tournaments... I never asked, but I am asking you now - what made you to assume that I didn't know all that stuff you're writing about?
All in all, you've written a lot, but didn't offer one single useful conclusion.
...

And what have I got? More of the same. You're still giving lectures to those ones who overslept lower grades of elementary school. You still haven't made a relevant claim. You still haven't offered one single useful conclusion. The few productive parts of your post address third grade problems...

Don't understand me wrongly - not reading carefully the post you criticize - is the sin we're both guilty of. But this time you crossed all boundaries. You pick a few sentences to quote and neglect to properly read even that tiny portion of text. Look at this:

Stephen Tu said:

Povratnik said:

Let's assume that every NS pair played the same contract. As it's already said - you have frequency advantage, I have points advantage. In this case, my advantage is clean ZERO. So your frequency advantage, no matter how small, literally guarantees you +EV.

Huh? WTF frequency vs. points? Let's say there are 100 other pairs, all in 4s, all play for the drop. You win 100 MP when you are right, when LHO is void. You lose 100 MP when you are wrong, when LHO has stiff K. There is no "point advantage" when everyone is in the same contract. It's just pure frequencies.

You're "correcting" me by saying in two sentences what I said in one! Yeah, I know, it was hidden in the middle. In sandwich between first and last sentence...

There is a comment where the first your sentence is "I don't get this argument at all.". In the last sentemce you said I was wrong. How do you know I'm wrong if you don't get it?

And this one really pissed me of:

Stephen Tu said:

Povratnik said:

You're trying to prove that trying to drop the West's king is clearly a better line than safety play, without EVER actually saying it. And you know what? Not only that you failed to convince me that your line is better; you didn't even convince me that it's your real opinion! I seriously tend to think that the main reason for your efforts is sheer inertia.

Huh? I thought I already stated this many times, fairly clearly. This is my claim:trying to drop west's stiff K yields more matchpoints than taking the safety play in the long run, if >= 89% of the relevant field is in 4S.

Or in other words, "IF 89+% of the field is in 4S, you SHOULD play for the drop", but "if <89 % of the field is in 4s, the others being in contracts yielding plus scores < 620, you SHOULD play safe".
Clear enough for you? I really don't get your complaints about my clarity or "may vs.should". Most everyone else on the thread understands what I meant.

A proper answer HAS to contain a clear message:
a) Yes, I AM claiming that cashing the ace is better line than safety play.
OR
b) No, I am NOT claiming that cashing the ace is better line than safety play.

Not only you haven't given a proper answer, you completely ignored everything that was said in the quote you picked yourself. You could well choose some other piece of my text and glue your mumbo jumbo as an "answer".
You're "claiming" that a player should always pick the line with greater mathematical expectancy. Really?
That's an insult. You should better not answer at all then "answer" this way. I never gave you an excuse (not to mention a real cause) to talk to me like that.
"I claim nothing. I am just making fun by discussing.", would be a disappointing, but honest answer. I would appreciate it.

There are some productive parts in your post, but they can wait. Now I have to ask you a direct question. (With the hope that I'll get a direct answer.)

Besides obvious generalities, the only thing you properly articulated was the claim that cashing the ace is legitimate line of play. Nobody disagreed.
Have you ever (in this thread) been trying to prove (or at least claim) ANYTHING more than that?

If the answer is affirmative, PLEASE be as precise and specific as you can.
If the answer is negative, PLEASE say it explicitely. I BEG you - don't throw at me another pile of trivial generalities as a replacement for direct and honest answer.

And finally, I'd appreciate if you don't answer immediately, but make at least a 24h delay... (Frankly, I am afraid of another mess)

Thank you for your time

[johnu]

Excuse me for intruding into this discussion but here are a couple of observations

Povratnik, on 2018-December-21, 21:58, said:

Stephen, you are VERY quick on trigger! There is no way you could read and assimilate such a big post in an hour, yet you immediately wrote a fairly long "answer". The result is very disappointing...

The timestamp on your big post was "Posted 2018-December-18, 17:09"
while Stephen Tu's response was "Posted 2018-December-18, 19:26"

That looks like 2 hours 17 minutes to me. That only tells me that Stephen is probably a fast typist, nothing more, nothing less.

[nige1]

Arithmetic isn't my long suit, so masochists are welcome to check my calculations..

Assume...
101 tables Match-pointed pairs .(American scoring: 1 for a win 0.5 for a tie)
You, South, declare 4♠.
The other 100 declarers also sit South.
All defenders lead ♣AK and another.
Declarer wins with dummy's ♣J.
Dummy leads ♠x and RHO follows low.
p of the other pairs bid 3♠ and go up ♠A.
q of the other pairs bid 5♠ and go up ♠A.
r of the other pairs bid 4♠ and go up ♠A.
s of the other pairs bid 4♠ and take the safety-play.
Note that p+q+r+s = 100.

Suppose you go up ♠A as Stephen Tu recommends

11% of the time, LHO is void, so you make 9 tricks and
- lose to p pairs, in 3♠.
- beat q pairs, in 5♠.
- tie r pairs, who go up ♠A in 4♠.
- lose to s pairs, who safety-play 4♠.

13% of the time, LHO has singleton ♠K, so you make 11 tricks and
- beat p pairs in 3♠.
- tie q pairs in 5♠.
- tie r pairs, who go up ♠A in 4♠.
- beat s pairs, who safety-play 4♠.

76% of the time, you take 10 tricks and
- beat p pairs in 3♠.
- beat q pairs in 5♠.
- tie r+s pairs in 4♠.

Hence, if you go up ♠A, then you score...
0.11 * (q + r/2)
+ 0.13 * (p + q/2 + r/2 + s)
+ 0.76 * (p + q + r/2 + s/2)
= 0.5 * ((0.26+1.52)*p + (0.22+0.13+1.52)*q + (0.11+0.13+0.76)*r + (0.26+0.76)*s)
= 0.5*(1.78*p + 1.87*q + 1.00*r + 1.02*s)
= 0.89*p + 0.935*q + 0.51*s + 0.50*r
= 0.89*p + 0.935*q + 0.51*s + 0.50*(100-p-q-s) (because p+q+r+s = 100)
= 0.89*p + 0.935*q + 0.51*s + 50 - 0.5*p - 0.5*q - 0.5*s
= 0.39*p + 0.435*q + 0.01*s + 50 MP

Suppose you take the safety-play as Povratnik recommends

11% of the time, LHO is void, so you make 10 tricks and
- beat p pairs, in 3♠.
- beat q pairs, in 5♠.
- beat r pairs, who go up ♠A in 4♠.
- tie s pairs, who also safety-play 4♠.

13% of the time, LHO has singleton ♠K, so you make 10 tricks and
- beat p pairs in 3♠.
- lose to q pairs in 5♠.
- lose to r pairs, who go up ♠A in 4♠.
- tie s pairs, who safety-play 4♠.

76% of the time, you take 10 tricks and
- beat p pairs in 3♠.
- beat q pairs in 5♠.
- tie r+s pairs in 4♠.

Hence, if you take the safety play, then you score
0.11 * (p + q + r + s/2)
+ 0.13 * (p + s/2)
+ 0.76 * (p + q + r/2 +s/2)

= 0.5 * (0.22+0.26+1.52)p + (0.22+1.52)*q + (0.22+0.76)*r + (0.11+0.13+0.76)*s)
= 0.5 * (2.00*p + 1.78*q + 0.98*r + 1.00*s)
= p + 0.87*q + 0.49*r + 0.5*s
= p + 0.87*q + 0.5*s + 0.49*(100-p-q-s) (because p+q+r+s = 100)
= p + 0.87*q + 0.5*s + 49 - 0.49*p - 0.49*q - 0.49*s
= 0.51*p + 0.38*q + 0.01*s + 49 MP

Thus, the safety play beats going up ♠A when
0.51*p + 0.38*q + 0.01*s + 49 > 0.39*p + 0.435*q + 0.01*s + 50 i.e...
0.12*p - 0.055*q > 1

If you judge that the field will play 4♠, then you should go up ♠A.
Also, If you judge that other pairs are likely to overbid, then you should go up ♠A.
Otherwise, you should take the safety-play when you guess that more than 8% of other pairs play in a partscore.

[Stephen Tu]

Povratnik, on 2018-December-21, 21:58, said:

Knock down without saying anything new, just by putting a quote from some of my previous posts...

Your attempts to knock down things are incredibly ineffective because of so much rambling and tangents. It's not clear what statement you are attempting to knock down at all. Quote a specific claim of mine, get directly to the point of why it is wrong, say how you would rewrite the sentence so that it is correct. From my point of view you haven't knocked anything down. Just made complaints about my writing style. Other people here don't seem to think it's unclear.

Quote

A proper answer HAS to contain a clear message:
a) Yes, I AM claiming that cashing the ace is better line than safety play.
OR
b) No, I am NOT claiming that cashing the ace is better line than safety play.

Wtf? I made my clear statement already, multiple times:


Don't play safe if >= 89% of relevant field playing 4s, for this particular board.


Do you agree with this statement or not, if yes, what are we arguing about; if no, rewrite the statement to what you think is correct.

Quote

You're "claiming" that a player should always pick the line with greater mathematical expectancy. Really?
That's an insult.

??? Why is that insulting? It's the correct answer to the question posed by the thread. And I attempted to show how to go about calculating it.


What am I supposed to claim instead?


Your "third part", I didn't address because I think I agree with it, at least the parts of it I was able to parse. But at the same time, since I was agreeing with it, I can't see that it was knocking down anything I said previously.


Mainly I am objecting to two claims of yours, which IMO are incorrect. I am not quite sure if you believe them in an absolute sense as you wrote then, or simply neglected to include appropriate caveats that would bring us into agreement.


One is that playing safe guarantees a good score regardless of field. And maybe regardless of board also, even when going for overtrick has bigger edge. Are you still claiming this, or did you not intend to mean this?



Your claim on surface appears to be "always play safe for games at matchpoints". Is this what you mean or not?



Also you seem to dispute that more people playing the same 4s contract as you does not favor the drop. Are you claiming this number has no effect at all, or the opposite, that more people in same contract favors playing safe?

My claim here is that the more people who are in 4s, the more points you gain not playing safe, when the drop was the right play, when k stiff offside. You are always comparing how many points you gain when you are right vs how many you lose when you are wrong, and the relative frequencies. Playing safe will swing more matchpoints when it is right due to outliers, vs what it loses when it is wrong, but that edge goes down as the number in 4s goes up, because that means the number of outliers is going down.

Playing safe or not is a board and field dependent decision. During play you can only guess at what the contract distribution is going to be. Only after scores are published do you find out whether your estimate was right or not.


Do you agree with this statement or not, or do you think it's always right to play safe, regardless of board or field?

[nullve]

I'm still surprised that people think a priori probabilities apply here.

If they do apply, then they also apply to the diamond suit, so there's a non-zero probability that West passed 1♠ with

♦QJT9876432

that has nothing to do with whether he was misbidding in some way. Hard to believe, isn't it?

[Povratnik]

@nige1

Sorry, you lost me at the very beginning. I don't understand that type of tournament. Against WHOM I can have win, tie or loss?
If that's essentially the same as team match with MPs counting, then your math is unnecessary, Stephen's line is definitely better. Can you make corresponding arithmetic for standard pairs tournaments?

@Stephen Tu

Since I have to write a short message to nige1, I'll take an opportunity to write one to you, in the same post.

Quote

??? Why is that insulting?

If you're so insensitive to insults, then it's a no brainer to me. I have a very effective answer:

Stephen Tu said:

"IF 89+% of the field is in 4S, you SHOULD play for the drop", but "if <89 % of the field is in 4s, the others being in contracts yielding plus scores < 620, you SHOULD play safe".

Povratnik said:

Nah, that's primitive. You should cover East's card when West is void, and put an ace when West has a king. This way you'll have MUCH better results!

If you turn out to be succesful in finding the flaws of my answer, but unsuccesful in finding the flaws of your statement, just report what have you found. I'll help you to find more.
Please don't write about anything else in your very next post. Just your thoughts about your statement and my answer.

EDIT: I am putting another message in this post

@nullve

You are trying to say that bridge inferences are more important than pure math?
I agree, but in this board you can't find anything useful, so we have to rely on good, old math...

[Stephen Tu]

The flaw of this particular statement (drop if stiff K if offside, play safe if lho void) is obviously that it requires omniscience. One can't take this (clearly optimal!) approach accurately unless you are a god and just know, or have unauthorized information about the board, from overhearing or perhaps seeing someone's scoresheet.

You are apparently implying that my approach also requires omniscience. This is not true. One can estimate the flatness of a board through experience. One can tell whether you or partner had borderline decisions, whether alternate contracts are particularly likely to be reached or not. Now certainly, one's estimate can turn out wrong, which can only be determined after the fact. More people can find a successful sac than you anticipated, which would make playing safe better. So what? Use the experience to refine your estimating skills, play safe the next time against similar board and field.

Surely taking such an estimate is the approach to deciding whether to play safe, rather than making blanket false statements about how playing safe for the contract will absolutely guarantee a good score, can never be bad, will always be above 50%, all of which you claimed. None of this is true, and is the main thing I dispute. You seem to advocate playing safe regardless of estimate of how flat the board will be, even on alternative board where playing safe costs an overtrick far more often than saving the contract, e.g. playing safe vs 4-1 breaks.

Now if you were just claiming that it's right to play safe on this board, because you think for certain > 11% are finding a successful sac, I wouldn't be fighting you.

I am fighting you because you seem to make blanket statements implying flatness of the board doesn't matter or is unknowable. You said +620 guarantees > 50% mp on the board which just isn't right.

[Stephen Tu]

And nige1 was just analyzing a standard pairs tournament. You can win tie or lose against each other pair playing the board. 1 point for win, half for tie. Add all comparisons together to get total number of matchpoints on the board.

Standard way to play matchpoint pairs (except that Europe often scores instead 2 for win, 1 for tie).

My math differed from his in that I assumed group Q in 5s was zero (presence of such a group clearly favors drop over safety play, as the drop never loses vs this group), and I used percentages of success accounting for the 3-3 club break rather than a priori percentages.

[nullve]

Povratnik, on 2018-December-22, 17:57, said:

@nullve

You are trying to say that bridge inferences are more important than pure math?
I agree, but in this board you can't find anything useful, so we have to rely on good, old math...

I'm only criticising the use of a priori probabilities here, as if the probability of a 0-3 diamond break isn't affected by the fact that West passed throughout.

Here are 100 hands dealt randomly on the condition that the NS cards are as above and West has ♠---♣AKx:

Spoiler

West hands:



   1.                  2.                  3.                  4.               
-                   -                   -                   - 
9 8 3 2             Q T 9 8 2           T 8 6 3             Q T 8 3 
Q T 6 4 3 2         Q J T 6 2           J T 9 7 6 2         J 8 6 4 3 2 
A K 5               A K 5               A K 2               A 6 2 

   5.                  6.                  7.                  8.               
-                   -                   -                   - 
T 9 8 6             T 9 8 6 2           8 6 2               Q 9 8 6 
Q 9 8 6 4 2         Q J T 9 2           Q T 9 7 6 4 3       9 7 6 4 3 2 
A 9 2               A K 2               A 6 5               A 9 6 

   9.                 10.                 11.                 12.               
-                   -                   -                   - 
Q T 3 2             Q T 6 2             T 8 6 2             Q T 3 
J T 9 8 7 4         J T 9 7 6 2         Q J T 9 6 3         Q J 9 8 6 4 3 
A K 2               A K 5               A 9 2               A 5 2 

  13.                 14.                 15.                 16.               
-                   -                   -                   - 
Q 9 3               Q 9 3 2             Q 8 6 3 2           Q T 8 3 2 
T 9 8 7 4 3 2       Q J T 9 6 3         Q J T 7 6           Q T 4 3 2 
A 9 6               A 9 5               A 6 5               A K 9 

  17.                 18.                 19.                 20.               
-                   -                   -                   - 
9 8 3 2             T 9 8 6 2           Q 8 2               9 8 6 3 2 
9 8 7 4 3 2         Q J T 7 6           Q T 8 7 6 4 2       J T 9 8 2 
A K 2               A 5 2               A 9 6               A 5 2 

  21.                 22.                 23.                 24.               
-                   -                   -                   - 
6 2                 Q 9 8 6 3 2         Q T 9 8 6 3         Q 8 
J T 9 8 7 6 3 2     Q J T 7             Q J 6 2             Q J 9 8 7 6 4 3 
A 9 6               A 6 2               A K 5               A K 6 

  25.                 26.                 27.                 28.               
-                   -                   -                   - 
Q T 9 8 6 2         Q 6 2               Q T 3 2             Q T 2 
J T 6 2             Q J 9 8 4 3 2       Q T 9 8 4 3         Q T 9 8 7 6 2 
A 5 2               A 9 5               A 9 2               A K 9 

  29.                 30.                 31.                 32.               
-                   -                   -                   - 
Q 9 8 6 2           Q 6 2               T 9 8 6 2           Q T 9 2 
Q J 7 6 3           J 9 8 7 4 3 2       Q J T 8 4           J 9 8 7 3 2 
A 6 2               A 5 2               A K 6               A 9 5 

  33.                 34.                 35.                 36.               
-                   -                   -                   - 
Q 9 8 3 2           T 9 8 6 2           Q 9 3 2             9 6 3 
J 7 6 4 3           Q T 7 6 2           Q J T 8 4 2         J T 8 6 4 3 2 
A K 9               A 5 2               A 9 6               A 6 2 

  37.                 38.                 39.                 40.               
-                   -                   -                   - 
Q T 8 3 2           Q T 6 3             Q 9 8 2             Q 6 3 2 
Q J 6 4 3           J 9 7 6 4 2         Q T 8 6 4 2         Q T 9 4 3 2 
A 5 2               A K 6               A 6 2               A 6 5 

  41.                 42.                 43.                 44.               
-                   -                   -                   - 
Q 9 8 3 2           Q T 8 2             Q 9 8 6             9 8 6 3 2 
Q T 8 7 3           Q J T 7 3 2         Q T 9 8 7 3         8 7 6 4 3 
A 6 2               A 6 2               A 9 2               A K 2 

  45.                 46.                 47.                 48.               
-                   -                   -                   - 
Q T 8 6 2           Q T 9 8 3           T 9 8 6 2           Q T 8 3 2 
J 9 6 4 2           J 8 7 6 2           J 7 4 3 2           Q 9 8 4 3 
A K 9               A 6 2               A K 6               A 6 2 

  49.                 50.                 51.                 52.               
-                   -                   -                   - 
T 8 3               Q T 9 8 6           Q 6                 Q T 3 
Q J 9 8 7 6 4       Q 9 7 6 3           J 9 8 7 6 4 3 2     T 9 8 7 6 4 3 
A 9 2               A 5 2               A K 2               A K 5 

  53.                 54.                 55.                 56.               
-                   -                   -                   - 
6 3 2               Q T 9 6 3 2         T 9 8 6 3           Q T 6 2 
J T 9 7 4 3 2       J 9 6 2             Q T 8 4 2           T 9 8 7 3 2 
A K 2               A K 6               A 6 5               A 9 5 

  57.                 58.                 59.                 60.               
-                   -                   -                   - 
Q 6 3 2             T 8 6 2             Q 8 3               T 9 6 2 
Q 7 6 4 3 2         J T 8 7 4 2         Q 8 7 6 4 3 2       Q J 9 6 4 2 
A 9 2               A 9 2               A K 9               A 6 5 

  61.                 62.                 63.                 64.               
-                   -                   -                   - 
T 9 6 3             Q 9 8 6             9 8 6 2             Q 9 6 3 2 
Q 8 6 4 3 2         Q J 6 4 3 2         J T 9 6 3 2         9 7 4 3 2 
A K 9               A K 2               A 9 6               A 6 5 

  65.                 66.                 67.                 68.               
-                   -                   -                   - 
9 8 2               Q 9 8 6             9 6 2               Q 9 8 3 2 
T 9 8 7 6 3 2       Q T 9 8 7 2         Q T 7 6 4 3 2       Q T 9 7 2 
A 6 5               A 9 6               A K 6               A 9 6 

  69.                 70.                 71.                 72.               
-                   -                   -                   - 
T 9 8 2             Q 8 3 2             Q T 9 8 6           9 6 3 2 
J T 8 4 3 2         J 9 7 6 4 2         T 9 8 7 3           Q J 9 6 4 3 
A K 2               A 9 2               A 9 6               A 9 6 

  73.                 74.                 75.                 76.               
-                   -                   -                   - 
9 6 3 2             Q 8 6 2             T 6 2               T 8 6 3 2 
Q J T 8 4 3         Q T 8 4 3 2         Q T 8 6 4 3 2       Q 8 7 3 2 
A 9 6               A K 2               A K 9               A K 5 

  77.                 78.                 79.                 80.               
-                   -                   -                   - 
Q T 6 3 2           T 9 8 6             T 9 8 6 2           Q T 8 6 3 2 
Q J T 9 3           J T 8 7 4 3         8 7 6 4 2           T 7 4 3 
A K 9               A 6 5               A K 6               A 9 6 

  81.                 82.                 83.                 84.               
-                   -                   -                   - 
9 8 3               Q 8 6 2             Q T 9 8 3           Q T 9 8 3 
Q J 9 8 7 6 4       T 9 6 4 3 2         Q 8 7 6 3           Q 8 6 4 3 
A K 9               A 9 6               A K 2               A 6 2 

  85.                 86.                 87.                 88.               
-                   -                   -                   - 
Q T 6 3             Q 9                 Q T 6               Q 8 3 
T 9 8 7 3 2         Q T 9 8 7 6 4 3     J 9 8 7 6 3 2       Q J T 9 7 6 3 
A 5 2               A 9 2               A K 9               A 6 2 

  89.                 90.                 91.                 92.               
-                   -                   -                   - 
T 6 3               9 3 2               Q T 8 6 3           3 2 
Q J T 6 4 3 2       J T 9 7 4 3 2       J 8 6 4 2           J 9 8 7 6 4 3 2 
A K 6               A 6 2               A 9 5               A 6 5 

  93.                 94.                 95.                 96.               
-                   -                   -                   - 
T 6 3               Q T 8 6             Q T 9 8 6           Q T 8 6 
J T 9 8 7 6 3       J 9 7 6 4 3         Q J 8 7 3           Q J 8 6 3 2 
A K 2               A 6 2               A 9 6               A 9 5 

  97.                 98.                 99.                100.               
-                   -                   -                   - 
Q T 6 3             T 8 6 2             T 9 8 2             Q T 8 3 
Q T 9 8 7 4         Q T 9 7 6 4         Q T 8 7 6 3         J T 9 8 7 6 
A 6 5               A 6 2               A 5 2               A 9 6 

Generated 5471 hands
Produced 100 hands

As West I would have acted on all of them at this vulnerability, either over (1♠) or over (1♠)-P-(4♠)-P; (P). You may think that's insane, but if these hands are representative and there's a chance that the actual West is anything like me, then the a priori probability of a 0-3 diamond break (~ 0.11) clearly doesn't apply, and I don't think it's even a good approximation unless the field is unrealistically timid or maybe unfamiliar with concepts like 'preempt', 'sacrifice' and (of course) 'Law of Total Tricks'.

[nige1]

Tramticket, on 2018-November-16, 06:29, said:

You have arrived in a good contract. The defence start with ace and king of clubs, followed by a third club won in hand with the queen (or won in dummy with the knave if you prefer?)..At IMPs, you take the safety play for one loser in trumps. What do you do at Match-point Pairs (mixed field)?

nullve, on 2018-December-23, 05:33, said:

I'm only criticising the use of a priori probabilities here, as if the probability of a 0-3 diamond break isn't affected by the fact that West passed throughout.
Here are 100 hands dealt randomly on the condition that the NS cards are as above and West has ♠---♣AKx:

Spoiler

West hands:



   1.                  2.                  3.                  4.   			
-       			-       			-       			- 
9 8 3 2 			Q T 9 8 2   		T 8 6 3 			Q T 8 3 
Q T 6 4 3 2 		Q J T 6 2   		J T 9 7 6 2 		J 8 6 4 3 2 
A K 5   			A K 5   			A K 2   			A 6 2 

   5.                  6.                  7.                  8.   			
-       			-       			-       			- 
T 9 8 6 			T 9 8 6 2   		8 6 2   			Q 9 8 6 
Q 9 8 6 4 2 		Q J T 9 2   		Q T 9 7 6 4 3   	9 7 6 4 3 2 
A 9 2   			A K 2   			A 6 5   			A 9 6 

   9.     			10.     			11.     			12.   			
-       			-       			-       			- 
Q T 3 2 			Q T 6 2 			T 8 6 2 			Q T 3 
J T 9 8 7 4 		J T 9 7 6 2 		Q J T 9 6 3 		Q J 9 8 6 4 3 
A K 2   			A K 5   			A 9 2   			A 5 2 

  13.     			14.     			15.     			16.   			
-       			-       			-       			- 
Q 9 3   			Q 9 3 2 			Q 8 6 3 2   		Q T 8 3 2 
T 9 8 7 4 3 2   	Q J T 9 6 3 		Q J T 7 6   		Q T 4 3 2 
A 9 6   			A 9 5   			A 6 5   			A K 9 

  17.     			18.     			19.     			20.   			
-       			-       			-       			- 
9 8 3 2 			T 9 8 6 2   		Q 8 2   			9 8 6 3 2 
9 8 7 4 3 2 		Q J T 7 6   		Q T 8 7 6 4 2   	J T 9 8 2 
A K 2   			A 5 2   			A 9 6   			A 5 2 

  21.     			22.     			23.     			24.   			
-       			-       			-       			- 
6 2     			Q 9 8 6 3 2 		Q T 9 8 6 3 		Q 8 
J T 9 8 7 6 3 2 	Q J T 7 			Q J 6 2 			Q J 9 8 7 6 4 3 
A 9 6   			A 6 2   			A K 5   			A K 6 

  25.     			26.     			27.     			28.   			
-       			-       			-       			- 
Q T 9 8 6 2 		Q 6 2   			Q T 3 2 			Q T 2 
J T 6 2 			Q J 9 8 4 3 2   	Q T 9 8 4 3 		Q T 9 8 7 6 2 
A 5 2   			A 9 5   			A 9 2   			A K 9 

  29.     			30.     			31.     			32.   			
-       			-       			-       			- 
Q 9 8 6 2   		Q 6 2   			T 9 8 6 2   		Q T 9 2 
Q J 7 6 3   		J 9 8 7 4 3 2   	Q J T 8 4   		J 9 8 7 3 2 
A 6 2   			A 5 2   			A K 6   			A 9 5 

  33.     			34.     			35.     			36.   			
-       			-       			-       			- 
Q 9 8 3 2   		T 9 8 6 2   		Q 9 3 2 			9 6 3 
J 7 6 4 3   		Q T 7 6 2   		Q J T 8 4 2 		J T 8 6 4 3 2 
A K 9   			A 5 2   			A 9 6   			A 6 2 

  37.     			38.     			39.     			40.   			
-       			-       			-       			- 
Q T 8 3 2   		Q T 6 3 			Q 9 8 2 			Q 6 3 2 
Q J 6 4 3   		J 9 7 6 4 2 		Q T 8 6 4 2 		Q T 9 4 3 2 
A 5 2   			A K 6   			A 6 2   			A 6 5 

  41.     			42.     			43.     			44.   			
-       			-       			-       			- 
Q 9 8 3 2   		Q T 8 2 			Q 9 8 6 			9 8 6 3 2 
Q T 8 7 3   		Q J T 7 3 2 		Q T 9 8 7 3 		8 7 6 4 3 
A 6 2   			A 6 2   			A 9 2   			A K 2 

  45.     			46.     			47.     			48.   			
-       			-       			-       			- 
Q T 8 6 2   		Q T 9 8 3   		T 9 8 6 2   		Q T 8 3 2 
J 9 6 4 2   		J 8 7 6 2   		J 7 4 3 2   		Q 9 8 4 3 
A K 9   			A 6 2   			A K 6   			A 6 2 

  49.     			50.     			51.     			52.   			
-       			-       			-       			- 
T 8 3   			Q T 9 8 6   		Q 6     			Q T 3 
Q J 9 8 7 6 4   	Q 9 7 6 3   		J 9 8 7 6 4 3 2 	T 9 8 7 6 4 3 
A 9 2   			A 5 2   			A K 2   			A K 5 

  53.     			54.     			55.     			56.   			
-       			-       			-       			- 
6 3 2   			Q T 9 6 3 2 		T 9 8 6 3   		Q T 6 2 
J T 9 7 4 3 2   	J 9 6 2 			Q T 8 4 2   		T 9 8 7 3 2 
A K 2   			A K 6   			A 6 5   			A 9 5 

  57.     			58.     			59.     			60.   			
-       			-       			-       			- 
Q 6 3 2 			T 8 6 2 			Q 8 3   			T 9 6 2 
Q 7 6 4 3 2 		J T 8 7 4 2 		Q 8 7 6 4 3 2   	Q J 9 6 4 2 
A 9 2   			A 9 2   			A K 9   			A 6 5 

  61.     			62.     			63.     			64.   			
-       			-       			-       			- 
T 9 6 3 			Q 9 8 6 			9 8 6 2 			Q 9 6 3 2 
Q 8 6 4 3 2 		Q J 6 4 3 2 		J T 9 6 3 2 		9 7 4 3 2 
A K 9   			A K 2   			A 9 6   			A 6 5 

  65.     			66.     			67.     			68.   			
-       			-       			-       			- 
9 8 2   			Q 9 8 6 			9 6 2   			Q 9 8 3 2 
T 9 8 7 6 3 2   	Q T 9 8 7 2 		Q T 7 6 4 3 2   	Q T 9 7 2 
A 6 5   			A 9 6   			A K 6   			A 9 6 

  69.     			70.     			71.     			72.   			
-       			-       			-       			- 
T 9 8 2 			Q 8 3 2 			Q T 9 8 6   		9 6 3 2 
J T 8 4 3 2 		J 9 7 6 4 2 		T 9 8 7 3   		Q J 9 6 4 3 
A K 2   			A 9 2   			A 9 6   			A 9 6 

  73.     			74.     			75.     			76.   			
-       			-       			-       			- 
9 6 3 2 			Q 8 6 2 			T 6 2   			T 8 6 3 2 
Q J T 8 4 3 		Q T 8 4 3 2 		Q T 8 6 4 3 2   	Q 8 7 3 2 
A 9 6   			A K 2   			A K 9   			A K 5 

  77.     			78.     			79.     			80.   			
-       			-       			-       			- 
Q T 6 3 2   		T 9 8 6 			T 9 8 6 2   		Q T 8 6 3 2 
Q J T 9 3   		J T 8 7 4 3 		8 7 6 4 2   		T 7 4 3 
A K 9   			A 6 5   			A K 6   			A 9 6 

  81.     			82.     			83.     			84.   			
-       			-       			-       			- 
9 8 3   			Q 8 6 2 			Q T 9 8 3   		Q T 9 8 3 
Q J 9 8 7 6 4   	T 9 6 4 3 2 		Q 8 7 6 3   		Q 8 6 4 3 
A K 9   			A 9 6   			A K 2   			A 6 2 

  85.     			86.     			87.     			88.   			
-       			-       			-       			- 
Q T 6 3 			Q 9     			Q T 6   			Q 8 3 
T 9 8 7 3 2 		Q T 9 8 7 6 4 3 	J 9 8 7 6 3 2   	Q J T 9 7 6 3 
A 5 2   			A 9 2   			A K 9   			A 6 2 

  89.     			90.     			91.     			92.   			
-       			-       			-       			- 
T 6 3   			9 3 2   			Q T 8 6 3   		3 2 
Q J T 6 4 3 2   	J T 9 7 4 3 2   	J 8 6 4 2   		J 9 8 7 6 4 3 2 
A K 6   			A 6 2   			A 9 5   			A 6 5 

  93.     			94.     			95.     			96.   			
-       			-       			-       			- 
T 6 3   			Q T 8 6 			Q T 9 8 6   		Q T 8 6 
J T 9 8 7 6 3   	J 9 7 6 4 3 		Q J 8 7 3   		Q J 8 6 3 2 
A K 2   			A 6 2   			A 9 6   			A 9 5 

  97.     			98.     			99.                100.   			
-       			-       			-       			- 
Q T 6 3 			T 8 6 2 			T 9 8 2 			Q T 8 3 
Q T 9 8 7 4 		Q T 9 7 6 4 		Q T 8 7 6 3 		J T 9 8 7 6 
A 6 5   			A 6 2   			A 5 2   			A 9 6 

Generated 5471 hands
Produced 100 hands

As West I would have acted on all of them at this vulnerability, either over (1♠) or over (1♠)-P-(4♠)-P; (P). You may think that's insane, but if these hands are representative and there's a chance that the actual West is anything like me, then the a priori probability of a 0-3 diamond break (~ 0.11) clearly doesn't apply, and I don't think it's even a good approximation unless the field is unrealistically timid or maybe unfamiliar with concepts like 'preempt', 'sacrifice' and (of course) 'Law of Total Tricks'.

Only 2 cases are worth simulation,

• West has a void in ♠
• West has a singleton ♠K

Neither is likely and all other cases result in the same number of tricks.

It isn't clear from Tramticket's original post that the opening leader held ♣K.
Anyway, Nullve's simulation confirms Stephen Tu's recommendation.

[PhantomSac]

If you would even consider safety playing on this hand, I would recommend a simple rule, never safety play at MP. That rule is probably wrong once every few years (depending on how much you play), so it won't be too far from wrong, and will prevent you from even thinking about ever making such a serious error as safety playing on this hand!

[nige1]

PhantomSac, on 2018-December-25, 16:09, said:

If you would even consider safety playing on this hand, I would recommend a simple rule, never safety play at MP. That rule is probably wrong once every few years (depending on how much you play), so it won't be too far from wrong, and will prevent you from even thinking about ever making such a serious error as safety playing on this hand!

Typical MP pairs problem.
You,West, declare 3N.
North leads ♠T and South follows with ♠6.
Plan the play

---

[PhantomSac]

nige1, on 2018-December-26, 22:36, said:

Typical MP pairs problem.
You,West, declare 3N.
North leads ♠T and South follows with ♠6.
Plan the play

---

If you choose to duck a club are you doing it because it makes it more likely that you "make your contract" or are you doing it because it is the percentage play to maximize your tricks? If the former then that is again a horrendous thought process. If you are in 1N or 2N your thought process should be the same on this hand as if you are in 3N.

Despite that, I did not say it is never wrong to safety play at MP, I said it is just almost always wrong and anyone who is considering doing it on this hand would be far better served to just never safety play. So if you find a hand where it is right to actually make a safety play in MP as opposed to your actual example, it still does not refute that.

FWIW IMO the most common time to safety play in MP is when you are in an extremely good situation that others dont rate to be in (like they have dropped a trick or 2 already that no one would, or you bid a slam with 15 HCP or something). I can't recall making a safety play in a normal contract. For example if your example hand had dummy with AKQxxx of clubs, ducking a club would be normal in imps since while it doesnt maximize your trick expectancy, it maximizes your chance to make your contract, but in MP it would be ridiculous.

[cherdano]

PhantomSac, on 2018-December-25, 16:09, said:

If you would even consider safety playing on this hand, I would recommend a simple rule, never safety play at MP. That rule is probably wrong once every few years (depending on how much you play), so it won't be too far from wrong, and will prevent you from even thinking about ever making such a serious error as safety playing on this hand!

Stronger words have never been spoken about a 2% edge!

[kuhchung]

omg what on earth did I just read