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x1S-43X analysis

Posted By: Nack Ballard
Date: Wednesday, 26 May 2010, at 6:46 p.m.

In Response To: 21S-43X question (Leonardo Jerkovic)

51S-43 [Z X8]

21S-43 [X Z2]

41S-43 [X Z34]

Leonardo asked, in addition to Z (reverse split, 24/21 13/9) being a good play, why is the tempo play of X (hit-and-split, 24/21 6/2*) also a good play for the middle position above (21S-43)? As a prelude to my own response, I created all three diagrams, asking which of Z or X is better and if the answer is the same for all three positions.

Leonardo's and Ian's answers demonstrated good comprehension for playing X in the third position: Leo said, "I can see merit of a tempo move in 41S due to powerful 9pt builder..."

Ian, after sharing that he had a predisposition towards Z in all three positions ("...I don't want to lose ground by getting hit back after 6/2*, and the loose hit on the two point also commits me to covering it when not hit"), added, "Having seen from the rollout that 21S-43[X=Z], the tempo-hit in 41S-43X must be better than 41S-43Z. After 41S, White is almost certain to make a good offensive point including better chances to point on Blue's split man, so taking that away has more value."

For 51S-43, the rollout for five plays (bot aggregate) is [U D7 S10 Z15 X23], but for purposes of this discussion I'm isolating just Z and X, where the former has a .008 edge, as indicated in the caption of the first diagram and repeated in the data summary below:

51S-43 [Z X8]
21S-43 [X Z2]
41S-43 [X Z34]

In the early game in general, deflecting the potent 9pt builder is often a fine, and in this case compelling, strategy. One should be much more willing to hit, anywhere, when the opponent has a 9pt builder than when she has a 10pt or 11pt builder (those two being close in deflectability value); less potent yet is a new builder / fourth checker on the 8pt (though since that can be freely used to make a second point with doublets it is more potent than no new builder at all).

As you can see, the X/Z margin for 41S-43 is .036 more X-supportive than that of 21S-43 (where the two plays are essentially tied). That's a larger than usual difference: the 9pt builder's usual point-making potency is magnified because it can actually be used to point on White, and there are a lot more ways that Blue can pick off the 16pt blot (than the 14pt blot) in an exchange of hits.

By contrast, the difference between the X/Z margins for 21S-43 and 51S-43 (positions repeated below) is only .010. But that difference is based on a lot of trials (i.e., it's not variance) and worth explaining. Where does X get off being equivalent in value to Z against 21S?

Most of the answer lies in the rolls of 63 64 41. If Blue plays Z (reverse split, 24/21 13/9), in the second position White can use her 11pt builder to make her 5pt or 7pt rather than merely hitting on the 4pt or making the 2pt.

Another reason that the tempo hit is useful is that it more often gives Blue a second crack at hitting an outfield blot whether he is himself hit or not. For example, after 21S-43X, White enters/runs with 61 63 or 64 and Blue rolls a 7 to hit; or White hits on her 23pt (instead of covering or using her 11pt builder) and Blue enters/hits with 65. Those variations are not as great an influence as they are in the comparison of other pairs of positions -- the 11pt builder is the hardest blot to hit; but they do exist here.

Nack

51S-43 [Z X8]

21S-43 [X Z2]

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