What's this 3S?

[barmar]

http://tinyurl.com/2dup2ll

 

With my club void, I figured the Moysian might work OK. I couldn't rebid my diamonds, as GIB thinks that shows 6-6 in the reds.

 

Why did GIB bid a 3-card spade suit when it had excellent support for my 2nd suit? 5♦ even makes if you guess trumps right (but I'd probably play 9-never and go down).

[arigreen]

GIB simulated among 3S,3N,4D,4H and found 3S to be the long term winner.

 

When opener was x64x, all bids except 4D led to a contract of 4H, usually making. Opener passed a 4D rebid.

 

When opener was 1543, opener bid 3N over 3S but 4H over 3N. 3N was usually the better contract.

 

 

The simulations here performed poorly for several reasons:

- GIB's understanding of the types of hands that bid 3D was poor. For example, GIB chose 3D with K.AQxxx.Axxx.QTx where most people would bid 3N

- GIB's predictions for how the auctions would continue was often incorrect. For example, correcting a 3N rebid to 4H but correcting a 3S rebid to 3N. Furthermore, in GIB's simulations partner never raised 3S to 4S, even when 3541. Thus the 3S bid was not penalized by the possibility of partner raising to 4.

 

 

As usual, the best fix for this sort of anomaly is improve the rules. In particular, the rule that dictates that GIB should bid 4♥ after P-P-1♥-P-2N-P-3♦-P-3N-P with 1543 should be removed. When I deleted this rule and reran the simulation, GIB bid 3N instead of 3♠ with the hand.

[cloa513]

And thats an improvement? with reasonable play and the obvious club lead 3NT has no chance 5D is the only one contract with a reasonable chance.

[arigreen]

Good point. In order to persuade GIB to pursue diamonds we need to further restrain opener's 3♦ rebid, to show a more distributional hand. In several of GIB's simulations, partner was 54 with mediocre diamonds and 3N was actually better than 5♦. Another fix would be to make 4♦ forcing so that GIB could bid 4♦ with this hand and land in 4♥ if partner is 64.