How to calculate variance of min. of N random variables?

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I have a realized dataset of random sample Y1 + Y2 ... + Yn from Exp($\lambda$) distribution. I want to estimate: $\mu$ = 1/$\lambda$

T = n * P where P is min for (Y1, Y2 ... , Yn) and is unbiased estimator for $\mu$ = 1/$\lambda$

How can I calculate Var(T) that is needed to calculate MSE(T)?