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61P-54 update

Posted By: Nack Ballard
Date: Saturday, 17 July 2010, at 6:34 a.m.

In Response To: 61P-54 update (David Rockwell)

Long ago, Stick and I estimated the misplay value for an opening 52. In round numbers, it was .01. This is about as big as it gets.

Hmm, .01 is a lot. Do you mean for the difference between 52D and 52S, or just for 52D?

I would expect that misplay differences in the opening are normally in the .000 to .002 range.

Sounds right. I once calculated 64P as gaining an extra .003 over 64S, back when opponents were more often mis-splitting in reply. I did this computation (using what I felt were aggressive-if-anything estimates of misplay probabilities for each roll against each play) for my own verification because a couple of experts, wild-eyed, were telling me how much unexpected equity they were gaining by playing opening 64P.

The real juice one gets is in playing rarely-if-ever-seen moves. Unfortunately, if you can on average induce additional errors of .011 or so by playing 32Z (reverse split 24/22 13/10, instead of 32S -- split 24/21 13/11) on the first roll, it still doesn't cover the .015 sacrificed. (If 32Z were also a contact-increasing move for long-term complications, one could easily piece together enough justification for playing it. It's close enough, though, that I think all one needs is to add some small intangible.)

I have frequently opened with 52D hoping for a misplay only to watch my intermediate opponent roll 31 while I waive goodbye to my gambit equity forever. I believe it is very difficult to play winning backgammon while making deliberate mistakes.

Agreed. But I think it's useful to distinguish between (a) immediate-error-inducing moves and (b) complicating moves (those that provoke hit exchanges or lead to priming battles). Either the superior or inferior player can benefit from (a), whereas (b) is typically in favor of the superior player.

Take opening 52$ (slot, 13/8 6/4), for example. For the stronger player, it has both (a) and (b) in its favor. While .05+ is more than I'm willing to sacrifice versus a much weaker opponent, I can't be 100% sure that 52$ is a poor opening gambit.

Nack

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