Tiger Double

[jdonn]

I think the above arguments involve the usually unrealistic assumption that the amount of tricks the opponents will make is predetermined to be equal at all tables (ignoring the impact doubling might have on that.) Why can't our opponents be in 4♠-1 when others are in 3♠-1? Every argument you guys are making begins assume this, assume that, if we assume the following, when frankly I don't particularly agree with any of the assumptions being made.

 

(You also ignore that doubling might make them take FEWER tricks. After all we have xx in trumps, this could easily induce a misguess.)

 

I think Phil's argument is fine. It's perfectly logical to deduce that when double would have been right we already had a good score, but when double would have been wrong our score wasn't going to be that bad. He just makes different assumptions than you (yours = people all make the same tricks, his = if this contract is normal then double is risky, and if its abnormal then double is unnecessary)

[pclayton]

If the rest of the field is in a making partscore then it really doesn't matter if you double. If they were going down then you would have had a top anyway, and if they make it then you would have had a bottom anyway.

 

Assuming that the double doesn't change the odds that they make it (not 100% clear I admit), you only have to compare the scores with the other pairs who are in game.

 

So if they make it more than 50% of the time then double will lower your expected MP score, and if they make it less than 50% of the time then double raises your expected MP score.

 

Of course, there may be a few other relevant contracts. For example, if other pairs are going down 800 in a partscore our way then double can cost but not gain. If other pairs misplay 3S for -1 then doubling can win but not lose. If some other pair is in 3NT+1 then doubling can only cost but if 3NT goes down 1 then doubling can only gain. Etc.

 

As Phil points out, 4S is likely either making or down 1. So at IMPs you would need better odds to double than at MPs, not the other way around.

 

edit: sorry Adam, I see you wrote the same. I'm a slow typer.

Han, if you can demonstrate with any degree of confidence that the opponents are playing or not playing in the field contract, I would agree with you. If you want to make spec doubles against contracts most of the field is in, go ahead, but I tend not to play 'tops and bottoms'.

[BillHiggin]

I covered 3 scenarios - double does not affect play, double helps declarer and double helps the defense. Yes, there was a bit of simplification for the first case - but the overall result is the same under that assumption. The other two assumptions are either big win or big loss situations and the math is rather trivial.

[awm]

The point I'm making is just this:

 

At matchpoints, you should double more aggressively if your opponents seem to be in a non-field contract.

 

Another way to put this is:

 

If, assuming everyone is in the same contract your opponents just bid, you think that doubling rates to be a winner, you should definitely double. In fact, sometimes it's right to double a non-field contract even if you wouldn't double if you thought everyone was there. The opposite, however (where you double if it's the normal spot but don't double if you think it's a non-field spot) should not happen.

[pclayton]

The point I'm making is just this:

 

At matchpoints, you should double more aggressively if your opponents seem to be in a non-field contract.

 

Another way to put this is:

 

If, assuming everyone is in the same contract your opponents just bid, you think that doubling rates to be a winner, you should definitely double. In fact, sometimes it's right to double a non-field contract even if you wouldn't double if you thought everyone was there. The opposite, however (where you double if it's the normal spot but don't double if you think it's a non-field spot) should not happen.

Adam what are you saying?

 

1 has nothing to do with 2, as far as I can see, although I tend to agree with 2.

 

1 seems to contradict what Han is saying.

[cherdano]

If the rest of the field is in a making partscore then it really doesn't matter if you double. If they were going down then you would have had a top anyway, and if they make it then you would have had a bottom anyway.

 

Assuming that the double doesn't change the odds that they make it (not 100% clear I admit), you only have to compare the scores with the other pairs who are in game.

 

So if they make it more than 50% of the time then double will lower your expected MP score, and if they make it less than 50% of the time then double raises your expected MP score.

This isn't quite true, because the likelyhood that game makes and the likelyhood that the other pairs are in game may be correlated.

 

Let me make a simple toy example: Let's suppose the rest of the field is completely uniform, will be playing in spades, and either all of them play in 3S or in 4S, and that the contract is either taking 9 or 10 tricks at all tables. Let's say the chance that the rest of the field is in game is 50%, and that we are

- 70% likely to beat it when the other pairs are not in game, and

- 40% likely to beat it when the other pairs are in game.

 

Then we are obviously more than 50% likely to beat it, but it is also obviously losing tactics to double.

 

Of course this is pretty artificial, but I think there is some truth to this model - if the other pairs are in game as well, there is a better chance that our opponents have judged correctly, and that game will make.

[han]

That is a good point Arend, but I think on this kind of auction (responder invites, opener reinvites, responder accepts) that effect is relatively small.