In: Statistics and Probability
Let X ∼ Poisson(λ) and Y ∼ U[X, 2X]. Find E(Y ) and V ar(Y ).
For a poisson distribution, the mean is equal to its variance which is equal to its parameter. Therefore, we have here:

Now, the conditional distribution of Y given X here is obtained as:

For compound distribution Y, the expected value and variance here are obtained as:




This is the required expected value of Y here.
Now the variance of Y here is obtained as:



The second moment of X here is obtained as:
E(X2) = Var(X) + [E(X)]2 = 
Therefore, we get the variance of Y here as:


This is the required variance of Y here.