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Explain Jacoby paradox

Posted By: leobueno
Date: Saturday, 8 December 2012, at 11:50 a.m.

Here is a Jacoby paradox example from Bob Koca [http://www.bkgm.com/articles/Koca/CuringYourShortBearoffBlues.html]. I suspect there are many others.

It's very unintuitive to think that one should double when the opponent's position improves, or conversely in this example, that it is OK to double when your winning chances are 55.4% but incorrect when your chances increase to 59.3%.

Will appreciate seeing an explanation.

The score (after 0 games) is: GNUbg 0, leobueno 0

Move number 4: leobueno on roll, cube decision?

GNUbg5

' ' ' '1X ' ' ' ' ' ' '

'1O ' '1O ' ' ' ' ' ' '
leobueno7
Position ID: EAAAiAAAAAAAAA Match ID: UQkAAAAAAAAE

• leobueno doubles

Alert: wrong double ( -0.076)!

Cube decision
2-ply cubeless equity +0.186
59.3 0.0 0.0 - 40.7 0.0 0.0
Cubeful equities:
2-ply cubeful prune [world class]
1.No double +0.187
2.Double, pass +1.000 +0.813
3.Double, take +0.111 -0.076
Proper cube action:No redouble, take (8.5%)

The score (after 0 games) is: GNUbg 0, leobueno 0

GNUbg4

' ' '1X ' ' ' ' ' ' ' '

'1O ' '1O ' ' ' ' ' ' '
leobueno7
Position ID: CAAAiAAAAAAAAA Match ID: UQkAAAAAAAAE

• leobueno doubles

Cube decision
2-ply cubeless equity +0.108
55.4 0.0 0.0 - 44.6 0.0 0.0
Cubeful equities:
2-ply cubeful prune [world class]
1.Double, take +0.111
2.Double, pass +1.000 +0.889
3.No double +0.108 -0.003
Proper cube action:Redouble, take

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