Cyberyeti, on 2011-May-26, 03:06, said:
If I had a singleton heart, I think I could bid 4♠ with impunity as now partner can have say ♥QJ109 and be thinking about doubling. As it is, he only has 3 so this is difficult to envisage (although if I had a void in spades opposite I might think about doubling to prevent partner doing something stupid, although I might then realise that thinking then passing might dissuade an ethical partner from bidding 4♠ on hands that should, so I might feel forced to X).
With the hand DBurn gave opposite, I think I'd X 4♥. I've overstated my hand with the jump to 3♠ and if I had the 2 minor suit Qs opposite I'd certainly expect to beat 4♥ or be getting a horrible result anyway if I didn't. Partner is more likely to have 18 or 19 points than 13 the way I think.
If we ran some simulations, I'm quite sure that 4♠ would come out on top as the winning option in the majority of cases where my vulnerable opponents have 22-27 hcp, a major fit, bid a game with apparent intent to make and I'm looking at a pretty certain minimum of 7 tricks for a -500 save. However, that isn't the test here. The question is does North's BIT suggest that 4♠ would be better than other logical alternative (e.g. pass)? Pass is going to win whenever 4♠x is going for 800 or when we can beat 4♥ and there will surely be a reasonably portion of hands where that is case; but this BIT by North undoubtedly tips the scales towards 4♠ being the superior choice.