In this problem, we would like to find the PDFs of order statistics. Let X 1 ,,X

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In this problem, we would like to find the PDFs of order statistics. Let X1,…,Xn be a random sample from a continuous distribution with CDF FX(x) and PDF fX(x). Define X(1),…,X(n) as the order statistics. Our goal here is to show thatfx(i)(x) = = n! fx(x) [Fx(x)]  [1 - Fx(z)]". (i-1)! (ni)! *

One way to do this is to differentiate the CDF (found in Problem 9). However, here, we would like to derive the PDF directly. Let fX(i) (x) be the PDF of X(i). By definition of the PDF, for small δ, we can write fx) (x)  P(x  X (i)  x + 8)d. Note that the event {x  X(i)  x +8} occurs if i - 1 of the X;'s are less than


Problem 9

In this prob lem, we would like to find the CDFs of the order statistics. Let X1,…,Xn be a random sample from a continuous distribution with CDF FX(x) and PDF fX(x).

Define X(1),…,X(n) as the order statistics and show thatn Fxs) (x) =  (7) [Fx(2)] * [1  Fx(x)]*-*. (i) k k=i

Fix x ∈ R. Let Y be a random variable that counts the number of Xj's ≤ x. Define {Xj ≤ x} as a "success" and {Xj > x} as a "failure," and show that Y ∼ Binomial(n, p = FX(x)).

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