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In a duplicate game today, my partner and I set our non-vulnerable opponents two for a score of +100. We got a bottom because other pairs with our cards earned part scores of 140. On the other hand, we would have earned a top if "down two" meant +200.This could come about if the opponents were vulnerable. And of course, down two doubled, non-vulnerable would be +300.

Is this result peculiar to the one game, or do good players follow a pattern of doubling in these types of situations when the opponents are non-vulnerable, while refraining from doing so when they are vulnerable. (The danger is that doubling may help the opponents make the contract or go down less.)

Also, would good duplicate players be more inclined to double non vulnerable opponents when the opposing contract was two of a major (+110) rather than two of a minor (+90)? (Rubber bridge players would be less inclined to double two of a major because of the risk of doubling the opponents into game)

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    You need to go buy and read Kit Woolsey's book Matchpoints - MP scoring should make you do all kinds of strange (to you) things like doubling contracts you're not so sure are going down (in certain situations). (and also not bothering to double contracts that you're almost sure will go down in other situations) Commented Feb 9, 2023 at 4:01

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You haven't told us the details, but, at any vulnerability, this could be a situation where you should double without even looking at your cards.

Let's suppose you magically know that every other pair playing your cards has been allowed to play 2S, but your opponents have bid 3D. Consider the scoring.

You don't know if 2S will make or go down, but suppose it's very unlikely to go down more than -100 (whether that's down 1 vul or down 2 nonvul). In that case, if they make 3D, then -110 will score 0 matchpoints for you. If you double and they make 3D, then -470 or -670 will score exactly the same 0 matchpoints for you.

On the other hand, suppose 3D goes down. Now of course if 2S goes down, it doesn't matter what you do, but if 2S makes for +110, doubling might take you from 0 matchpoints for +100 to all the matchpoints for +200 or +300. (It could also take you from 0 matchpoints for +50 to 0 matchpoints for +100. In fact, it's more important to double if opps are vulnerable because it's reasonably frequent that it actually improves your score.)

This means, in this situation, doubling is free. It will never hurt your matchpoint score (the lingo I learned is that it turns your 0 into a rounder 0), but can improve it. Hence you should double without looking at your cards.

Now of course, in reality, probably not all other tables will play in 2S, so the odds are not quite as dramatically in your favor. (Also, in reality, bidding 3S is an option if you think both 3D and 3S are likely to make.) You should still double when the odds are slightly against setting the contract - what is meant by 'slightly' depends on your estimate of what the other players playing your opponents' cards will do.

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  • "This means, in this situation, doubling is free. It will never hurt your matchpoint score,,,, but can improve it. Hence you should double without looking at your cards." Good point. Basically the gist of the question. As you said previously, "110 is better than 100" so if the opponents deprive you of 110, you must make them pay 200, not 100 for doing so, in order to come out ahead.
    – Tom Au
    Commented Feb 10, 2023 at 4:09

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