Question

Consider a random sample $Y_1, Y_2, \dots, Y_n$ from a continuous population with mean $E(Y_i) = \mu$ and finite variance $V(Y_i) = \sigma^2$. Show that the estimator $\frac{1}{n}\sum_{i=1}^n (Y_i - \overline{Y})^2$ is a biased estimator for $\sigma^2$.

          Consider a random sample $Y_1, Y_2, \dots, Y_n$ from a continuous population with mean $E(Y_i) = \mu$ and finite variance $V(Y_i) = \sigma^2$. Show that the estimator $\frac{1}{n}\sum_{i=1}^n (Y_i - \overline{Y})^2$ is a biased estimator for $\sigma^2$.
        
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Consider a random sample Y1, Y2, …, Yn from a continuous population with mean E(Yi) = μ and finite variance V(Yi) = σ^2. Show that the estimator (1)/(n)∑i=1^n (Yi - Y)^2 is a biased estimator for σ^2.

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Elementary Statistics a Step by Step Approach
Elementary Statistics a Step by Step Approach
Allan G. Bluman 9th Edition
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Consider a random sample Y₁, Y₂, ..., Yₙ from a continuous population with mean E(Y) = μ and finite variance V(Y) = σ². Show that the estimator S² = 1/(n-1) Σ(Yᵢ - Ȳ)² is a biased estimator for σ².
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Transcript

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00:01 Here in the first part, if i is not equal to j, then expectation of xi and xj is equal to expectation of xi multiplied with expectation of xj since they are independent and we have this is equal to mu square since expectation of exi is equal to mu for all i's.
00:34 If i is equal to j, then expectation of xi xj is equal to expectation of xi whole square plus variance of xi which is equal to mu square plus sigma square as since variance of xi is equal to sigma for all i, sigma square for all i therefore, e or expectation of xi comma xj is equal to mu square if i is not equal to j, mu square plus sigma square if i is equal to j...
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