Suppose we know p(x,y), p(x,z) and p(y,z), is it true that the joint distribution p(x,y,z) is identifiable? I.e., there is only one possible p(x,y,z) which has above marginals?
distributions
mathematical-statistics
user1466742
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Jawaban:
Consider the random variables(Y1,Y2,Y3) which are uniformly distributed on the set {(1,0,0),(0,1,0),(0,0,1),(1,1,1)} . These have the same marginals as (X1,X2,X3) .
The cover of Douglas Hofstadter's Godel, Escher, Bach hints at the possibilities.
The three orthogonal projections (shadows) of each of these solids onto the coordinate planes are the same, but the solids obviously differ. Although shadows aren't quite the same thing as marginal distributions, they function in rather a similar way to restrict, but not completely determine, the 3D object that casts them.
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In the same spirit as whuber's answer,
Consider jointly continuous random variablesU,V,W with joint density function
It is clear thatU,V , and W are dependent
random variables. It is also clear that they are not
jointly normal random variables.
However, all three pairs (U,V),(U,W),(V,W)
are pairwise independent random variables: in fact,
independent standard normal random variables (and thus
pairwise jointly normal random variables).
In short,
U,V,W are an example of pairwise independent but not
mutually independent standard normal random variables.
See this answer of mine
for more details.
In contrast, ifX,Y,Z are mutually independent standard normal random variables, then they are also pairwise independent random variables but their joint density is
sumber
You're basically asking if CAT reconstruction is possible using only images along the 3 main axes.
It is not... otherwise that's what they would do. :-) See the Radon transform for more literature.
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