[Bbradley62]

Shouldn't
p-(p)-1m-(2M)-2N
be weaker than
p-(p)-1m-(2M)-3N?

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[barmar]

This is another case where there are a variety of rules that lead to the 3NT bid, and some of them require extra strength, while others don't. As a result, the description is the least common denominator.

[Bbradley62]

As a passed hand, North can't have any more strength than 11 HCP and 12 total points, so I'm puzzled as to what those "extra strength" options might be. My question is: what would North have done if his ♦K had been ♦x instead? Or if he held ♠KQxx, ♥xxx, ♦xxx, ♣QJT? Would he have passed, intending to pass a re-opening double? I'd want to bid 2N with those hands, but I'm sometimes very mama-papa in my approach.

[barmar]

The problem is that the criteria in the rules don't distinguish passed vs unpassed hands. It would be enormous work to go through all the rules lke this, splitting them up into separate cases just to make the explanations clearer.

The actual fact is that there's no rule matching the North hand, so the book bid is to pass, but simulations told it to bid 3N. Then it displays the description going with the rules that DO generate 3NT.

[Bbradley62]

It might also be interesting to know why North chose 3N after the 1♦ opening but 2N after the 1♣ opening.

[xxhong]

I think 1C contains a lot more balanced minimum hands than 1D.

Bbradley62, on 2011-November-08, 12:32, said:

It might also be interesting to know why North chose 3N after the 1♦ opening but 2N after the 1♣ opening.

[barmar]

Or maybe it's more worried about the ♦Kx when partner hasn't shown anything in ♦.

As I said, simulations were used for these auctions, so they're sensitive to the hands in the samples, and different auctions will result in different samples. And even within a given auction, there's no clearcut bid. I tried it will 11 different random seeds, and got the following distribution of bids:

With the 1♣ opening: IMPs: 2x2N, 5x3♣, 2x3N, 2xPass. MP: 4x3♣, 1x3N, 6xPass
With the 1♦ opening: IMPs: 4x2N, 5x3N, 2xPass. MP: 4x2N, 2x3N, 5xPass

I was surprised that MP still had so many 3♣ bids, since matchpoints puts a high premium on major and NT contracts. I expected most of them to migrate to 2NT.