[機統] 統研所考題
請教各位:
(1)在Cauchy分配下,樣本平均與任一樣本的m.g.f相同故由唯一性推得分配亦相同.
為何中央極限定理在Cauchy分配不成立的理由與m.g.f相同有關?
(2) U1,…,Un~U(0,1) (iid),求Π(1 - Ui/n)之極限分布?
用到定理解題: if lim E(Un) = a , lim Var(Un) = 0, then Un conv to a in
square mean.
在計算Var(Π(1 - Ui/n))時, 當中需計算 E(1 - Ui/n)^2:
我是把平方式展開個別算得值為1 - 1/n + 1/3n^2 ; 解答表示成 1 - 1/n + o(n)/n
想請問o(n)/n 是怎得出?又Var(Π(1 - Ui/n))如何計算至0?用我自己算的值,求不出0
(3) X1,…,Xn~U(0,θ) (iid),θ1 = n+1/n max(X1,…,Xn).求n(θ1 - θ)之極限分布?
我是令Yn = n(θ1 - θ),最後用 order statistics求P(θ1 < θ + y/n)時
對於θ + y/n之範圍的找法不知道該如何找
(4) Suppose X1,…,Xn have P(Xi = 1) = p,P(Xj = 0) = 1-p,P(Xi = 1,Xj = 1) = q,
whenever i is not equal to j.Find Var(X1 + … +Xn).
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◆ From: 59.120.241.229
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(4)要問的是
E(Xi)可否用Xi=0計算?Xi,Xj是給定的嗎?
Cov(Xi,Xj) 可否計算出P(Xi=0 ,Xj=0) = 1 - q - 2p(1 - p)代入?
Var(Xi)可否用Bernoulli試驗來算(把Xi當成試驗1次: Xi=1表示成功, Xi=0表示
失敗)?
※ 編輯: Rotman 來自: 59.120.241.229 (06/28 16:07)
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剛才想通疑惑了...沒注意到i與j不相等以致多考慮到獨立情形
題目也奇妙在取值0與1使得E[Xi]=E[Xi^2],如果取值非0與1,這題要如何解?
※ 編輯: Rotman 來自: 59.120.241.229 (06/29 15:05)
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