Team IMPS & safety plays:when are they worthwhile?

[luke warm]

~snip~

Under this third and final assumption, we can conclude that P0>P1>P2...>P10 and that P0 and P1 are pretty similar. This leads us to P1 being roughly (1/11) times P0+P1+P2...+P10, or perhaps a little more than that. So if the contract goes down without the safety play one time in twelve, we have (1/12)(P0+P1+...+P10) is about the same as (11/12)(P1) and the safety play is about break-even.

sorry for snipping your earlier comments, it's to save space.. it was all very intersting.. but what does it boil down to, adam? take this example... it's the first board, you're in 4♠ and you have 9 tricks in the bag...

 

you have the ♦AQx on the board, and you're leading from your hand... assume you honestly have no clue who has the king... the odds are 50/50 on the finesse for the overtrick... do you take the finesse?

 

maybe the ones who say to always play for the overtrick are right, i don't have the skills or experience to know first hand... but intuitively it seems to me that to risk a game bonus (what, 7-10 imps?) on a 50/50 shot that gains at most 1 imp seems frivilous to me

 

'course my intuition isn't right nearly enough, so it could be wrong here

[Al_U_Card]

~snip~

Under this third and final assumption, we can conclude that P0>P1>P2...>P10 and that P0 and P1 are pretty similar. This leads us to P1 being roughly (1/11) times P0+P1+P2...+P10, or perhaps a little more than that. So if the contract goes down without the safety play one time in twelve, we have (1/12)(P0+P1+...+P10) is about the same as (11/12)(P1) and the safety play is about break-even.

sorry for snipping your earlier comments, it's to save space.. it was all very intersting.. but what does it boil down to, adam? take this example... it's the first board, you're in 4♠ and you have 9 tricks in the bag...

 

you have the ♦AQx on the board, and you're leading from your hand... assume you honestly have no clue who has the king... the odds are 50/50 on the finesse for the overtrick... do you take the finesse?

 

maybe the ones who say to always play for the overtrick are right, i don't have the skills or experience to know first hand... but intuitively it seems to me that to risk a game bonus (what, 7-10 imps?) on a 50/50 shot that gains at most 1 imp seems frivilous to me

 

'course my intuition isn't right nearly enough, so it could be wrong here

Not quite the same as a safety play at 4% likelihood......take the finesse and bear the brunt of your teams wrath....

[awm]

sorry for snipping your earlier comments, it's to save space.. it was all very intersting.. but what does it boil down to, adam? take this example... it's the first board, you're in 4♠ and you have 9 tricks in the bag...

 

you have the ♦AQx on the board, and you're leading from your hand... assume you honestly have no clue who has the king... the odds are 50/50 on the finesse for the overtrick... do you take the finesse?

 

maybe the ones who say to always play for the overtrick are right, i don't have the skills or experience to know first hand... but intuitively it seems to me that to risk a game bonus (what, 7-10 imps?) on a 50/50 shot that gains at most 1 imp seems frivilous to me

 

'course my intuition isn't right nearly enough, so it could be wrong here

Assuming it's an 11 IMP swing if I go down (this will depend on vulnerability of course), then I should be willing to take a 1/12 chance of a set in order to get an 11/12 chance of an overtrick, assuming it is the first board of a match against an equal team.

 

The finesse example, I am taking a 1/2 chance of a set in order to get a 1/2 chance of an overtrick, so this is obviously lousy odds.

 

All of this comes to the following:

 

If you are playing a fairly long match against an evenly matched team, and the state of the match is equal (i.e. board one), then the strategy that maximizes your expected IMPs is extremely close to also maximizing your chances of winning.

[Trumpace]

If you are playing a fairly long match against an evenly matched team, and the state of the match is equal (i.e. board one), then the strategy that maximizes your expected IMPs is extremely close to also maximizing your chances of winning.

Suppose we are concerned solely with the boards where there is an 8% chance of throwing away 11 IMPS but 92% chance of gaining 1 IMP (assuming opp plays for safety).

 

Also, assume that of all the bridge deals that are possible (which is a finite number, though very large) around 1.1 percent (I am making this up, just to get a point across) are the 8% 1 vs 11 IMP deals.

 

Consider playing a "fairly long match" of 1000 boards.

 

How many such 8% deals do you expect to occur among the 1000 boards? 11 right?

 

Now if there are 11 such 8% 1 vs 11 IMP boards, the chances of gaining IMPS on these boards by playing safe is 61% (as calculated on a previous post).

 

So if you use your long run strategy (maximising expected IMPS per board) for a 1000 board match, I can beat you (assuming we are equally matched) with 61% chances by playing safe for the 8% 1 vs 11 IMP boards, while using the same strategy as you on the remaining boards!

 

If the match was say a million trillion boards long, you will probably win if I stuck to playing safe on the 8% boards. (Haven't calculated...)

 

The reason the 1%, 2%, 3% IMPS add up is that, in shorter runs too, they actually give more than even chances.

 

The point is that even though the whole match might be long... the number of boards of a particular kind (here 8% boards with 1 gain vs 11 lose IMP) might be small enough to require an approach other than just the long run analysis.

[awm]

You're assuming that these "safety play" boards are the only swing boards in the match. Combined with the (likely) assumption there are only a small number of them, this effectively creates a short match in which each board has only two possible outcomes. This will give you a distribution that does not look (at all) like the one I have postulated, where (for example) win by two is slightly less likely than win by one.

 

I don't believe these are reasonable assumptions. In fact, I believe that even in a 12 board match between evenly matched teams, the outcome probabilities will be such that win by X is always at least as likely as win by X+1, for any choice of X. Obviously you can construct contrived examples where this is not the case -- for example if you play 11 boards and every board is either win 11 or lose 1, then win by one is much more likely than a tie (actually ties are impossible) and win by 13 is much more likely than win by 12 (actually win by 12 is impossible). But I think realistic matches even of 12-24 boards in length will in fact have the property I am using.

 

Anyways, my analysis requires the bold face assumptions, and while I think they are very reasonable, you are welcome to try to come up with examples where they don't hold (and try to argue that those examples are reasonable).

[Trumpace]

You're assuming that these "safety play" boards are the only swing boards in the match. 

I am not assuming that at all. I am saying that I dont need to assume that.. I can play with such a strategy which will make those 11 8% boards the only boards that count!

 

quoting myself...

So if you use your long run strategy (maximising expected IMPS per board) for a 1000 board match, I can beat you (assuming we are equally matched) with 61% chances by playing safe for the 8% 1 vs 11 IMP boards, while using the same strategy as you on the remaining boards!

 

Basically for boards other than the 8% boards I will play with the same strategy as you do. For the 8% boards I will play safe, in effect giving me a 61% chance of winning. By using your strategy on all but the 8% boards, in effect, I have made these boards decide the outcome of the match!

[Trumpace]

Anyways, my analysis requires the bold face assumptions, and while I think they are very reasonable, you are welcome to try to come up with examples where they don't hold (and try to argue that those examples are reasonable).

I am not saying that the long run analysis won't work! All I am saying is that there is more to it than just maximising the expected number of IMPS per board.

 

The reason I need to contrive values is that it is very hard to show real bridge situations where the long run analysis might fail. These are not sufficient grounds to declare that the arguments I am making are bogus...

 

As a fair approximation, using the long run analysis is probably good enough (though not in all cases, which is my point), as there are other factors which are more important in deciding the outcome of the match.

 

Don't just blindly use "in the long run it wins hence I use it" approach. Though it might work for most cases, the reasoning is still wrong! That is all. You might turn out to be right, but there could be cases where it is the wrong thing to do! If your opponents just find one such case (which I admit, would probably be pretty hard to do), they can beat you if you blindly stick to the 'in the long run' strategy.

[Joe de Balliol]

Well, in the Portland Bowl last year Oxford B won two matches by 2 IMP

 

My first-round NICKO match this year was tied after 24 boards and went to a tie-break.

 

Everyone's drawn some Swiss teams matches.

 

In my Crockford's Cup match this year my team was playing against Forrester, Mizel, Allfrey, and Tosh. After 8 boards we were 57 IMP down. While we 'only' lost by 70 or so overall, for boards 9 onwards the idea was to lose by as little as possible, hence it was purely take the odds as we had no chance of winning and knew it.

 

Finally - I think the contract matters. Safety plays are not usually best in part-scores, worth taking in games, should be taken in slam, and should generally be taken in grands unless the chance of an overtrick is VERY high :P

 

J

[mikeh]

Safety plays are not usually best in part-scores, worth taking in games, should be taken in slam, and should generally be taken in grands unless the chance of an overtrick is VERY high B)

 

I would be very interested to see a 'safety play' that would be appropriate in a grand :D

[Blofeld]

Clearly he means you shouldn't be playing for a procedural penalty in your favour if it risks the contract.

[42]

I would be very interested to see a 'safety play' that would be appropriate in a grand B)

You have 2 possibilities:

1. trump the missing A with undoubtable emphasis and play the rest of the cards in superhighspeed mode, or

2. keep the opp with the missing A off from lead (using Luis' army sunglasses and rejecting the lead from the other side in the above mentioned manner), after Murphy's law his partner leads the only suit that guarantees the grand.

But before you decide for the appropriate safetyplay (keeping in mind the ASL-rule), flip a loaded 70g silver coin 3-7 times (depends on whether you are born in the year of the ape or not, ask Dr. Ruth!) with putting back and be sure that you hit the TD 3-7 times on the same place of his temple.

Treat both opps between all that flipping to

a.) if male: 3-7 big glasses of fine Rum and a big Havanna (wellknown as Fidel-Coup), and 100 pictures of Nikki Diamond,

b.) if female: expensive narcotic Parisian fragrance, the latest COSMOPOLITAN plus BEAUTIFUL LIVING and pruning shears,

c) if mixed and longtime couple: a small silver pistol with a guide for Russian Roulette together with some rat-poison in a beautiful wooden box (can be used later for jewelleries or bolts and nuts, depends...),

d) if mixed and fresh in love: a first aid packet for lovers and a credit note for a weekend in a nice hotel in Venice plus entry fee for the local 22 boards bridge tourney.

That makes in total 99,999period% (the missing 0,00000.....1% can definitely be neglected, serious studies proved that).

GL!

[ardf10987]

(Joe de Balliol @ Dec 23 2005, 11:43 AM)

Safety plays are not usually best in part-scores, worth taking in games, should be taken in slam, and should generally be taken in grands unless the chance of an overtrick is VERY high...

(mikeh @ Dec 23 2005, 07:07 PM)

I would be very interested to see a 'safety play' that would be appropriate in a grand

Obviously I would be equally interested, in a grand, to see the chance of an overtrick... B)