dake50, on 2012-August-02, 20:27, said:
They've bid 3H. I think 18 trumps so I bid 3S.
RHO also thinks 18 that may be 8 for Spades 10 for Hearts so 4H.
Now partner also thinking 18 maybe 10-8 bids 4S.
Now LHO agrees 4S may make so 5H is cheap.
So this decision was REALLY bid to 5H-X.
Was some "law" reasoning wrong??
Yes.
The first line is usually fine, bid 3S.
The second is twisted, but with possibly the correct answer. 18 means :
1) if they make 10 for 170, we make 8 for 2 off, and this is usually bad. Only OK if they don't double and we are not vulnerable
2) if they make 9, for 140, so bid 4H and we make 9 for one off, and that's OK for a better score unless we are vulnerable and they double
3) if they make 8, for one off, we make 10 and get our game : so bid game as it scores more
Assign weights to the 3 lines, maybe 60% for the 9-9 trick split and 20% for each of the others, and see what the expected outcomes are for making the bid as opposed to passing or doubling.
All lines may lead to the same conclusion, but vulnerability must be considered (no point in -500 when they would otherwise get +170), and the indications of high card strength (if you have all the values you bid game anyway, and if they have more than you the expected penalties become severe).
The third line is twisted and with possibly the wrong conclusion. The legal thoughts are :
1) 18 means if they make 10, we make 8, and unless adverse vulnerability that's OK, so bid 4S
2) if they make 9, we make 9, so by bidding 4S I am trading a positive for a negative. At any vulnerability, so don't bid it.
3) if they make 8 we make 10, so while our game makes, double perhaps scores better at this vulnerability
The fourth line is definitely wrong.
1) If 4S makes 10, 5H is going 3 off for 800 or 500. OK only if favourable vulnerability, bad on all other.
2) If they make 9, we are trading a positive for a negative
3) if they make 8, we are trading a positive for a negative
You have to do the sums, and it depends on vulnerability. Assume they are going to double you when you overbid (they always double me).
It also depends on your expectation of the hcp split between you and them (eg do you have 6 or 10 hcp opposite partner's opening?), and if you know from the bidding that they have values sitting on top of yours, or vice versa. The expectation is only 9 tricks - 9 tricks if points and positional values are equal. If not, instead of considering the results for 10-8, 9-9, and the 8-10 trick split, you need to work out for example the results from 9-9, 8-10, and 7-11. This now brings in the possibility of your 3S bid pushing them into a very good game they might not otherwise bid.
While you should consider all the expected scores from the expected permutation of trick splits, and assign weights to give your the overall expectation of success, a rule of thumb is if all is equal :
a) bid to your legal level if you have the higher ranking suit,
b) bid to one higher than your level if needed and you have the lower ranking suit,
c) double them if they bid higher than you.
Also remember that you can only estimate the total number of tricks. While you may know you have a 9 card fit, theirs might not be.
And that doubling opponents in 3H does not go down well with team-mates if it makes 9 tricks.