Posted 2010-October-10, 12:31
MP: Same as IMP, play absolutely safe (because the contract is 5♥, but gamble if it were 4♥).
On trick expectation gambling for 10 tricks or 12, versus safe for 11, is obviously a somewhat close question
By my calculation the best gambling line is strip then spade finesse, 21% for 12 tricks and 18% for 10, but the exact result doesn't matter, only that it's close enough that, correctly (which I think it is) or not, some 4♥ declarers will gamble.
For the sake of MP strategy we can put aside the hands that make 11 tricks and assume the gamble matters. Just assume we make 10 or 12 tricks about equally often, about half of (the relevant) time each.
Against the 4♥ declarers who gamble we are in terrible shape. If we play as they do, we expect only about 1/4 of the matchpoint -- half when making 12 tricks but nothing when making 10 tricks. Comparatively our expectation by playing safe is much better even though it is less than 1/2.
Against the 4♥ declarers who play safe, we would get a slight edge by gambling but not nearly enough to compensate for what it costs us against the gambling 4♥ declarers.