Talk:Conditional independence

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Contents 1 Good Examples Link 2 Graphic of Squares 3 Independence 4 Unclear Baysian networks

[edit] Good Examples Link

http://www.dcs.qmul.ac.uk/~norman/BBNs/Independence_and_conditional_independence.htm Davyzhu (talk) 06:05, 27 February 2008 (UTC)

Conditional Dependence links to the butterfly effect? That seems kind of absurd! That article hardly discusses conditional dependence and is totally different. I think we should have this page discuss both conditional dependence and independence. I changed the link to link here, and renamed the link to the butterfly effect.Epachamo 00:16, 20 April 2007 (UTC)

[edit] Graphic of Squares

I cannot verify that P(AUB|not C) in the first figure is equal to P(A|C)*P(B|C). I count that P(AUB|not C) is 4/37, P(A|notC) is 12/37, and P(B|notC) is 12/37. That doesn't work out. Did I miss something? 76.8.64.166 (talk) 20:51, 16 January 2008 (UTC)

Agree, the graphic is incorrect. It would be valid if the grid were 6x8 instead of 7x7, with other areas unchanged, then fractions are 12/36 x 12/36 = 4/36 167.136.242.40 (talk) 22:57, 18 February 2008 (UTC)dfry

Yeah, the graphic is incorrect !!! —Preceding unsigned comment added by 58.161.42.51 (talk) 00:54, 8 May 2008 (UTC)

[edit] Independence

I have been told that two variables can be indendant, but not conditionally independant. For example, if a variable Z is dependant on two variables X and Y, and X and Y are independant, then X and Y are *not* (or may not be) independant given Z. Is this true? If it is it should be explained in this article. Fresheneesz 01:55, 1 December 2007 (UTC)

Example proving that two variables may not be conditionally independant even if they are unconditionally independant:

X – 0 or 1 (random coin flip)

Y – 0 or 1 (random coin flip)

Z – sum of X and Y (can be 0, 1, or 2)

X and Y are obviously independant. P(Z==0)=0.25, P(Z==1)=0.5, P(Z==2)=0.25 . Knowing what Z is will enable you to know something about what X is if you know what Y is - in some cases allowing you to know exactly what X is. Thus X and Y aren't conditionally independant given Z. Fresheneesz 03:30, 1 December 2007 (UTC)

[edit] Unclear Baysian networks

The section on Baysian networks is exteremly unclear, and poorly constructed. It is always a bad idea to begin with an example. The addition of the "frequentist" further confuses the section. Fresheneesz 02:11, 1 December 2007 (UTC)