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Cross IMP's

#1 User is offline   patrickC 

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Posted 2004-January-04, 18:30

I am trying to understand this. Is it better to play the "middle"?
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#2 User is offline   inquiry 

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Posted 2004-January-04, 21:55

Hi,

I think it depends upon what you mean by cross imps and the strategy you want to employ. If you play in an 8 board imp tournment with 40 tables, you will not win playing down the middle unless you get a couple of gifts. The reason being that someone is getting gifts and eight boards is not enough to make up for gifts you are not getting.

If on the other hand, you are just playing in the open room, or you are playing in a long event (18 boards or more), playing down the middle is probbly the best strategy, at least early. Of course if you think you are plus a few imps with a few boards to play, strategy comes into play again.

Ben
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#3 User is offline   Free 

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Posted 2004-January-05, 01:33

When playing cross imps, you can lose a lot in a strong field, and win few! If everybody wins 4H and you don't bid 4H or play -1, you lose imps against EVERY other pair! This also means an overtrick can give you some imps, but the contract is still the most important.

The way I usually play cross imps is: play like a team match, but if you have a 100% line for = and a 90% line for +1 (10% -1 or more) I go for the 90% line to win something, unless I think nobody else bid that good contract... Also, if you didn't bid game and you see you can always make ur game, go for as much overtricks as possible (damagecontrol, just in case).
"It may be rude to leave to go to the bathroom, but it's downright stupid to sit there and piss yourself" - blackshoe
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#4 User is offline   patrickC 

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Posted 2004-January-05, 07:47

Those messages really helped me. Thanks so much!!
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#5 User is offline   mikestar 

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Posted 2004-January-05, 17:52

IMPs were devised as a compromise between match points and total points--cross IMPs shifts the line just a bit closer to the MP end of the spectrum. Free is right on the money. In total points, I don't take a 99.5% line for +1 if it risks a sure game, in match points I'll take a 51% line if it is a normal ocntract.
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#6 User is offline   Gerardo 

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Posted 2004-January-05, 23:09

I think what in BBO it is called "Cross IMPs" in some places, it is just normal IMPs, not Crossed

#7 User is offline   Cascade 

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Posted 2004-January-06, 05:20

Quote

I think what in BBO it is called "Cross IMPs" in some places, it is just normal IMPs, not Crossed


Cross Imps in a pairs game means that your score is IMPed against every other table and then divided by the number of other tables (or maybe one less).

Other Imp pair games are possible. Butler Pairs or Datum Pairs the table scores are averaged and your score is compared to this average (or the 'Butler' ;-) )

Wayne
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Posted 2004-January-06, 06:54

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IMPs were devised as a compromise between match points and total points--cross IMPs shifts the line just a bit closer to the MP end of the spectrum.  Free is right on the money. In total points, I don't take a 99.5% line for +1 if it risks a sure game, in match points I'll take a 51% line if it is a normal ocntract.


Time to argue sematics.

If you play 100 4H vul contracts with 100% line that always wins 10 tricks, and 99% line (we will drop the .5%) that wins either 11 tricks or 9 tricks (+650 - 100), then in total points or imps, the clear winner in the long run is the 99.5% llne. For you win (or avoid losing) 1 imp 99 times and lose 12 imps once. That is a net gain of 87 imps. From a total point perspective, 99x650 - 100 = 64250, where as 100x620 = 62500.

This suggest that "winning bridge" in the long run if you could work out the odds of 99.5% chance for +1 suggest taking the "gamble". But the best advise would be to take the sure line at imps as you suggest, since the opponents might not bid game however, there maybe some other unusual circumstances that affect your decision (see comment below).

Further, of course, this assumes you can calculate the odds correctly each time and that all your opponents get to game (especially in a cross-imp thing). IF even a few fail to bid game, you win plenty of imps just for making your 10 tricks.

Which brings us to Free's original comment. "The way I usually play cross imps is: play like a team match, but if you have a 100% line for = and a 90% line for +1 (10% -1 or more) I go for the 90% line to win something". At 90% I think this is wrong, especially in a cross imps. Let's do the match. You win 90 imps on the 90 times this makes an extra trick, but you lose 10 x 12 imps (or 120 imps) when it is wrong. So going for the extra trick wiht 90% odds is mathematically wrong (net minus 30 imps). Total points? 90x650 - 10x-100 = 57500 while playing for 10 sure tricks averages 62500.

This is even bigger wrong in cross imps. In a large field like we have in BBO with highly varied skilled level, there is a premium just for bidding the "normal game". A fair number of pairs will fail to bid the extemely obvious game and many will manage to go down by failing to find either line you think about. A vul game even missing the extra trick rates to win imps. To risk the sure win of imps in a BBO cross imp thing for a 90% chance for a potential overtrick isn't mathematically sound in the first place, and at cross imps with so many tables, is very unwise, imho.

Now in a close match against a good team, or in a one board tie-breaking playoff, by all means, you can take what ever chance you think makes good bridge logic.

Ben
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#9 User is offline   Gerardo 

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Posted 2004-January-06, 13:15

I see, the only place I saw Cross IMPs was in old WinBridge, where no division took place, so I take back my comment

Thanks Wayne

#10 User is offline   Cascade 

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Posted 2004-January-06, 14:23

Gerardo, on Jan 6 2004, 04:15 PM, said:

I see, the only place I saw Cross IMPs was in old WinBridge, where no division took place, so I take back my comment

Thanks Wayne

Using cross-imps you do not need to divide. That is the what is used in the Cavendish Pairs and maybe some other events where hundreds of IMPs swing.

Wayne
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I believe that the USA currently hold only the World Championship For People Who Still Bid Like Your Auntie Gladys - dburn
dunno how to play 4 card majors - JLOGIC
True but I know Standard American and what better reason could I have for playing Precision? - Hideous Hog
Bidding is an estimation of probabilities SJ Simon

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