Consider the following family of distributions:P = {Pλ(X = x) : Pλ(X = x) = λxe−λ/x!; x = 0, 1, 2, . . . ; λ = 0 or 1} .This is a Poisson family with λ restricted to be 0 or 1 . Show that the family P is not complete,demonstrating that completeness can be dependent on the range of the parameter.
Question
Consider the following family of distributions:P = {Pλ(X = x) : Pλ(X = x) = λxe−λ/x!; x = 0, 1, 2, . . . ; λ = 0 or 1} .This is a Poisson family with λ restricted to be 0 or 1 . Show that the family P is not complete,demonstrating that completeness can be dependent on the range of the parameter.
Solution
To show that the family P is not complete, we need to find a non-zero function g(X) such that E[g(X)] = 0 for all λ in the parameter space, but g(X) is not identically zero with probability one.
Let's consider the function g(X) = X - λ.
For λ = 0, we have E[g(X)] = E[X] = λ = 0.
For λ = 1, we have E[g(X)] = E[X - 1] = λ - 1 = 0.
So, E[g(X)] = 0 for all λ in the parameter space. However, g(X) is not identically zero with probability one because X can take on values other than λ.
Therefore, the family P is not complete. This demonstrates that completeness can be dependent on the range of the parameter.
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