[TrampledUF]

I've played duplicate for 5 years with the Jacoby 2NT convention, I obsessively play BBO anonymous hands on my phone, but I can't recall ever seeing a slam contract reached after a Jacoby 2NT bid. Why is it so rare? What is your experience?

[etha]

I can sim this if you want. What conditions do you want random hands where Jacoby is used or random hands where Jacoby is used and there is a slam?

[etha]

hmm having trouble simming it cos its so rare amusingly. :-)

[etha]

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Ok try this one second hand I got it to use Jacoby.

[etha]

Ok I dealt 23k hands

0.235% went 1spade 2nt. 0.196 % bid small slam


which seems a lot that wld mean 84% of hands where Jacoby is used jack bids 6.

[TrampledUF]

Ok, so that's 0.25% of hands where someone has a 1H opener and not contested?

So that sounds like if I dropped the convention, then each time partner or I opens 1M, there's roughly a 1 in 200 chance we're missing out on a Jacoby path to slam.

[etha]

no that was 0.25 % of hands that are dealt result in 1♥ 2nt i'm just revising my values the spade one above is right I think but it does seem weird

[etha]

Jacoby seems to be a tiny fraction of dealt hands is sort of the problem only say 70 hands are 1♥ 2nt out of the 23k.

[etha]

you might of course use Jacoby more or less than my definitions which are all 12+ HCP with 4 trumps and all 8+ HCP with 14+ total including distributional points.


I can see what percentage of hands bid Jacoby when 1♥ is opened.

[etha]

4.4 % of hands are being opened 1♥

[etha]

and 3.75% of those bid jacoby

[etha]

hmm and my numbers for hands that bid slam after Jacoby are just rubbish which explains why it was so high.

[etha]

ok I found a bug so I gave up with uncontested and exhaustively checking the auction and I just dealt some hands and am dbl dummy seeing if there is a slam which shd be good enough.

[etha]

ok so the rough and ready answer is 46/100 1♥ Jacoby auctions lead to a dbl dummy makeable slam for your side. and 41/100 for spades.

Which is still oddly high but the method was not bugged this time I'm pretty sure.

Sample sizes were not very big but that probably doesn't matter.

[etha]

Of course I have no idea how many of those are biddable using Jacoby. I could run it but would take a while. And I could then run them again having deleted Jacoby from the CC.


Hope that was some use in the end.

[thepossum]

TrampledUF, on 2019-March-07, 11:14, said:

I've played duplicate for 5 years with the Jacoby 2NT convention, I obsessively play BBO anonymous hands on my phone, but I can't recall ever seeing a slam contract reached after a Jacoby 2NT bid. Why is it so rare? What is your experience?

EDITED to remove waffle

Hi TrampledUF and Etha

Very interesting topic and analysis. Surprising how rare they seem to be. Without simulation and simply understanding the use of the convention, when its used, how rare it is etc. I suspect what you are looking at is, as Etha says, simply that firstly Jacoby is rare, not everyone plays that system, thirdly slams are a small percentage of major contracts so you are looking at a small percentage of a rare bidding sequence. And on top of that any individual observer only sees a tiny percentage of those hands. So all in all a very unlikely thing to observe.

Etha's sim show 70 hands out of 23K (although that does seem very low, but I havent simmed it, but it will be small and I trust the number ).

Then, how many hands does each individual see/play in a year say. I've been playing and watching intensively for say 8 months. Maybe 3 hours per day -> 30 hands per day -> 30*240 = 7200 hands in 8 months or over a year 10800 hands etc. And then you have to assume that you spent all that time looking for that sequence and noticing it, lets say the chance of observing one when it happens (and noting it) is 10% (rubbery figure No 1)

That gives 70/23000 * 40%(chance of making) * 10800 (hands observed) * 0.1 (hands registered and remembered) = approx 1.3 slam Jacoby hands/per annum occurring and noticed by any individual on average (with a very high variance I assume).

Then, of course, humans are less "accurate" in bidding than a robot on average so are probably less likely to bid one that is theoretically possible from a simulation. Most players are not experts or advanced enough to bid them as often as they could. You need access to real data to evaluate it ( a bit like Pavlicek's or Kidd's analyses). I believe, reading Kidd on LaJolla's site (based partly on Garvin and Pavlicek's data) that expert players only bid and make approx. 50% of DD theoretical available slams (EDIT Ignore this last figure. Its my interpetation from graphs). And of course there is the unknown percentage of players who play Jacoby 2NT.

From Kidd's figures - Low rank players only make slams out of approx <1% of hands, average players approx 2% of hands, and World class approx 5% of hands compared to double dummy approx 14% of hands. This is reading from a graph so not accurate figures - please refer to Kidd

Also, according to Kidd many players in different forms of play will stop in game rather than going to slam. It depends on the percentage of the slam, the scoring, state of tournament etc

It was a very interesting question from TrampledUF and answer from Etha. Many lessons and implications in it for many application areas and perceptions throughout the world which impact on decision making, politics, everything etc

The literature of Rare Event Modelling may be somewhat relevant although a Jacoby slam bid is rather less critical than an earthquake, tsunami or coup d'etat

Note I also ran a very crude and brief frequency analysis (using bdeal) on Jacoby shape NS hands (5-card major) such that EW are unlikely to open or interfere. My sim backs up Etha's (no doubt much better) sim. My hand generation gave approx 0.15% (crude) Jacoby heart/spade shape and the double dummy slam success rate (12/13 tricks) was approx 30% +/- 2% 95% CI for hearts and spades, 51% +/- 2% (95% CI) for either. Of course that assumes they were bid which I didnt analyse

It would be great if anyone could actually get any real figures on slam success with Jacoby

regards P

Refs

La Jolla (Kidd, M.)

Pavlicek

Slam statistics - Kidd

[TrampledUF]

Interesting, everyone. Thanks!

[thepossum]

Hi

I was sitting at a table of World Class and/or Expert players the other day and this hand came up. I'm not sure on the etiquette of posting other players hands so I have left the players anonymous but they were all top players

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It was last hand, one of the kibitzers said 6H to finish perhaps. West bid 1H, North passed, East bid an alerted artificial bid as Jacoby style. South interfered with a cue, West bid 5H which was passed

Double dummy gives this 12 tricks on almost any lead and 13 on a low spade

West made 5H+1 on a heart lead

I checked the traveller. Only one table (out of 15) bid Jacoby 2NT managed to get to 6H and managed to make it One other table reached slam by other means and went down 1

All other Easts bid variants on 4H, 4NT, 3NT, 1NT etc, some tried slam and stopped in 5. Nobody managed to show their control in diamonds and try slam. The Jacoby table ignored the missing control and gambled.

I'm not expert enough to know but maybe 2NT gets in the way of a well-ordered slam auction and control bidding and maybe also it invites interference with top players, and maybe most players dont use it much

regards P

EDIT I apologise. I fixed an error with the two slam tables. I mixed them up.

[hrothgar]

thepossum, on 2019-March-14, 17:44, said:

maybe 2NT gets in the way of a well-ordered slam auction and control bidding and maybe also it invites interference

Whether or not the opponent's interfere is going to depend on a number of factors including

1. Their shape
2. Their strength
3. The amount of bidding space that they have available
4. Whether or not we have shown a fit
5. How much strength our side is known to have

In the case of a Jacoby 2NT

The bid has no impact on items 1 or 2

J2NT uses up a fair amount of bidding space. It forces the opponents to make a bid of 3!C plus. Arguably, this makes it more difficult to intervene

J2NT shows a fit, which might make it easier for the opponents to compete

J2NT promises game forcing values and establishes a forcing pass which makes it more dangerous to compete
On balance, I think that it is often harder to compete over a J2NT bid than many other options with the same hand.

FWIW, playing MOSCITO, after a major suit opening we have both relays and a J2NT type bid available, the reason being that making a relay with a big fit often leads to preemption while we experience less interference after the J2NT bid.

[thepossum]

Thx Hrothgar

I have edited since I had an error. The one table who used it, did bid to slam but ignored the missing control. My memory plays up sometimes and I confused the two slam hands

But all your points are still valid, despite my errors.

Maybe only a top player could compete over it in this case

"If a tree falls in a forest and no one is around to hear it, does it make a sound?"