Basic IMP strategy

[thepossum]

Hi all

 

I asked a similar question recently about strategy at MPs between staying in game and bidding slam.

 

Here is a similar scenario which occurred recently in a small IMP tourney

 

I will post the hand in a little while but a crude post hoc simulation of the scenario has suggested to me that the probability of the major slam is of the order 60% and game was near certainty (eg >98.5%). Assuming I could work that out in my head how do I then make the decision in an average field of how to proceed. Is 60% reasonable or not

 

You estimate that p% of the field will bid slam and (1-p)% will bid and make game

 

You decide (without the probability) after a keycard ask, and a few concerns about 1 missing keycard, and too many losers in your hand to stop in 5. Note it was likely to be a 4-4 H fit and hands were fairly flat with possible spade shortage in North and both hands roughly in 14-16 range, your is 17 :) EDIT It was south who investigate the slam with Blackwood and made the call in most cases

 

The hand is played and you score -5 IMPs. Those who bid and made slam scored 9 IMPs. Both sides vulnerable. Ignoring two outliers who bid and made a different (minor) slam P was around 1/3 and Q around 2/3. 100% of people made 12 tricks! Ratio 13:2:28

 

What are the considerations at IMPs. I nearly went for it but didnt.

 

Hand will be posted soon

 

regards P

[smerriman]

At IMPs, the decision is simple. You bid a major suit slam if it makes at least 50% of the time - fullstop.

 

See details here.

 

The rule of Blackwood - if you use Blackwood and find you're missing one keycard (and not the queen of trumps), always bid slam, 100% of the time. If you're uncertain about slam when missing one keycard, then you can't use Blackwood - you have to investigate via another route.

[thepossum]

Thanks Stephen

 

I'm very curious about it since so many players didnt even investigate slam, a few who did investigate (including myself) stopped in 5, but most who investigated did go to slam. Note we did have the Queen of trumps and I usually go to slam missing only 1 key card but not the Queen. I must have imagined a problem somewhere

 

Maybe I saw a risk in the hand that wasnt there. Just by way of possibly irrelevant information I looked at the stated expertise of players and their BBO masterpoints. There was no significant difference on mean masterpoints, no real difference in median masterpoints, ie those who bid slam did have more masterpoints on average. There was some evidence of difference between number of players in Expert, Advanced, Inteermediate categories, with Advanced and Intermediate twice as likely to stop in game and experts about 50:50

 

I'm very curious about all this. Clearly on the expected IMPs from my example the 50% you cite seems correct to balance up the chance of positive score. However I am also interested in how it relates to the quality of the field etc.

 

Normally I'm more of a risk taker than this but I must have seen something at the time :)

 

P

 

Note. Everything I'm testing is underpowered and probably has errors since there clearly seem to be differences that dont show statisticaly yet :) I need more data and adjustments. Still honing my approach. This is just one hand and 42 tables

[smerriman]

However I am also interested in how it relates to the quality of the field etc.

As per the PDF above, it doesn't. It's completely independent - regardless of whether everyone else is in 1♥, everyone else is in 6♥, or anything in between, you should still bid 6♥ if it makes 50% of more of the time.

[thepossum]

Hi Stephen

 

I'm still unsure. I understand maybe what you say (and the document) relates to pure IMP scoring comparing two teams. But at cross IMPs surely the scores depend on the number of tables which bid the game vs the slam which in turn relates to how the field assesses the hand which in turn relates to the quality of the field. I understand the difference between the top and the bottom on any particular hand relates to the pure IMPs but in an overall tournament sense its more complex and depends on how the rest of the field goes. Maybe I dont fully understand how it works. But if a smaller percentage bids and makes then your negative score in relation to the field is less than if a large percentage makes it. Does all maths behind it simplify to 50% irrespective of the quality of the field? I need to study it more

 

But clearly Bob Hamman knows the correct strategy in bidding slams :)

 

regards P

 

PS Here is my hand and the bidding. I was somewhat unsure what GiBs 3S alerted bid meant other than a force in hearts. Its not the Stayman followup I am used to but I did know it was enough to investigate slam. I was not able to ascertain position of Kings which is why I stopped

 

[hv=pc=n&s=saq2hkq42dkjt5cq3&d=s&v=b&b=7&a=1n(15-17)p2c(Stayman)p2hp3s(Forcing%20H%20raise%2015%2B%20pts)p4n(RKCB)p5h(2%20keycards)ppp]133|200[/hv]

 

Note. Edited to fix the 3S bid. Thx Stephen :)

[Stephen Tu]

It really doesn't matter what percentage of field is in slam. Your gain when it works is (+13 x people in game)/total comparisons. Your loss when it fails is the mirror (-13 x people in game)/total comps. The breakeven is when these are equal frequency, 50%.

 

The exact amount of imps you lose to the people in game will vary a bit depending on how much of the field is in slam. But the breakeven for profit (50%) will work out the same.

As for your auction, presumably GIB bid 3s not 2s as your diagram indicates. Probably NT bidder is not supposed to assume captaincy here; just cue bid 4d. Partner knows more about your hand than you do about his, so let him take control (though GIB isn't going to do as well as a human expert).

 

In general, if you ever use keycard, and despite finding your side holds 4/5 keycards and Q of trumps(or 10 cd fit), and you don't bid slam, you have made a mistake at some point. If you take control and find only one ace missing bid slam, if it goes down either it was unlucky layout, or you weren't actually supposed to take captaincy, or someone misbid earlier, or sometimes the hands just happened to mesh poorly and your system wasn't good enough to really find this out.

On this hand partner is allegedly showing 15+; 32 pts and not missing 2 keycards or 1 keycard+Q is good slam typically.

 

 

[thepossum]

Hi Stephen

 

Thx. The problem was bidding the cues under GiB's system. Cue bids would have been Aces not kings :(

 

There was a reason I couldnt investigate with cues

 

P

[Stephen Tu]

GIB lies sometimes, you can lie also. Or cue 4s perhaps.

But haven chosen RKC, don't stop if not missing 2 KC or 1KC + trump Q.

 

[thepossum]

Yes, 4S would have been a good option, or I should try showing AK cues to cover one or the other (although 4D could be risky if North uses Blackwood). Maybe North would then have started RKCB

 

They were possibly in a better place than me to assess slam but still had two possible diamond losers

 

Note usually I would take 3S as a natural forcing bid but from the GiB alert I couldnt really infer anything about distribution other than 4+ hearts

 

[hv=pc=n&s=saq2hkq42dkjt5cq3&n=s4ha875dq76cakj75]133|200[/hv]

[smerriman]

There's really not much you can do, simply because GIB's cuebidding is awful. With a human, you bid 4D (or 3N if you play that as a max) and it's easy after that.

 

With GIB, I'd just bid 4NT, knowing it's terrible but that there's nothing better, then bid slam and hope they have clubs stopped.

[thepossum]

Thx Stephen