X1ï¼X2ï¼â¦â¦ï¼Xnç¸äºç¬ç«ï¼
并ä¸è½å¾å°Xiä¸Xçåå¼ç¸äºç¬ç«ã
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Xi-Xçåå¼
=Xi-1/n·(X1+â¦â¦+Xn)
=(n-1)/n·Xi-1/n·(X1+â¦â¦+Xn)
ãåé¢çæ¬å·é没æXiã
â´D(Xi-Xçåå¼)
=(n-1)²/n²Â·D(Xi)+1/n²Â·[D(X1)+â¦â¦+D(Xn)]
=(n-1)²/n²+1/n²Â·(n-1)
=(n-1)/n
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