I have a sample of about 1000 values. These data are obtained from the product of two independent random variables ξ∗ψ. The first random variable has a uniform distribution ξ∼U(0,1). The distribution of the second random variable is not known. How can I estimate the distribution of the second (ψ) random variable?
Answer
We have, Assuming ψ has support on the positive real line,
ξψ=X Where X∼Fn and Fn is the empirical distribution of the data.
Taking the log of this equation we get,
Log(ξ)+Log(ψ)=Log(X)
Thus by Levy’s continuity theorem, and independance of ξ andψ
taking the charactersitic functions:
ΨLog(ξ)(t)ΨLog(ψ)(t)=ΨLog(X)
Now, ξ∼Unif[0,1],therefore−Log(ξ)∼Exp(1)
Thus,
ΨLog(ξ)(−t)=(1+it)−1
Given that Ψln(X)=1n∑1000k=1exp(itXk),
With X1...X1000 The random sample of ln(X).
We can now specify completly the distribution of Log(ψ) through its characteristic function:
(1+it)−1ΨLog(ψ)(t)=1n1000∑k=1exp(itXk)
If we assume that the moment generating functions of ln(ψ) exist and that t<1 we can write the above equation in term of moment generating functions:
MLog(ψ)(t)=1n1000∑k=1exp(−tXk)(1−t)
It is enough then to invert the Moment generating function to get the distribution of ln(ϕ) and thus that of ϕ
Attribution
Source : Link , Question Author : Andy , Answer Author : Drmanifold