Responding 3NT to a Preempt

Three hands with a similar theme have cropped up recently:

1.        S: 963
          H: 9
          D: K7654
          C: AKQ3
 S: AKT2           S: J84
 H: K53            H: QJT842
 D: AQT2           D: 9
 C: 52             C: JT6
          S: Q75
          H: A76
          D: J83
          C: 9874

North opened 1, I overcalled 3 as East and partner bid 3NT to play. Oppo started off with a couple of rounds of clubs but then got bored and switched and partner wound up with an overtrick. You may not agree with my choice of overcall, but give me an extra heart and it makes no difference to the outcome — 4 is substantially the better contract.

2.        S: KJ98765
          H: 9
          D: 42
          C: 743
 S: A              S: 42
 H: KJT852         H: Q74
 D: Q6             D: KJT983
 C: T952           C: AK
          S: QT3
          H: A63
          D: A75
          C: QJ86

At our team-mates' table, North opened 3 in first, East passed and South tried 3NT. Not a great success as you can see. 4 has no chance either but it's a lot fewer undertricks.

3.        S: 9743
          H: AJ98752
          D: K
          C: 9
 S: A8             S: QT52
 H: 43             H: 
 D: A9642          D: QJT5
 C: Q652           C: KJ843
          S: KJ6
          H: KQT6
          D: 873
          C: AT7

At a friend's table, North opened 3 in first, East passed and South tried 3NT rather than the raise. It worked out fine on a low diamond lead, but could have gone horribly wrong with 4 excellent.

Bad luck or bad judgement? Let's give our partners some likely hands for their preempts and simulate how the two strains compare.

On the first hand, with LHO opening 1 and partner overcalling 3, I ran 1000 tests. On 498 of those, both contracts failed or both contracts made. However, on every single one of the remaining 502 deals, 3NT went off with the major game making. Never was 3NT better. In terms of IMPs (and I assumed that we were vulnerable for all tests and never doubled), playing in hearts scores you a whopping 7.4 IMPs/board. The reasoning, I suppose, goes as follows: if partner has good enough hearts to run then it's highly unlikely that he's able to stop the club suit.

Next, the spade preempt and again 1000 tests were carried out. This was a lot closer. In fact, the raise to 4 won by only a single case. On 187 occasions the major game was making with 3NT failing, while on 186 the reverse occurred. The rest of the time, both contracts made or both went off. The IMPs score was more favourable to those playing in suit contracts, though, with an average gain of 1.9 IMPs/board. This reflects that, while it's fairly even in terms of purely making your contract, 3NT is likely to go off more and those vulnerable undertricks can add up.

And finally, the other heart preempt when we had that four-card support. This time, of the 1000 tests, 40 resulted in a game swing for 3NT, 330 for raising to the heart game, while the other 630 were more neutral. In all, you gain an average of 5.5 IMPs/board by playing in hearts.

Obviously, the oppo may well have a blind lead. On hand 1, a club lead might not be obvious from a lot of North's holdings and 3NT will sneak home. Nevertheless, I think that a figure of 7.4 IMPs/board is pretty convincing, as is 5.5 IMPs/board for hand 3. Hand 2 is much closer.

Generalisations to follow. Some day. If you're lucky.