3. Typically, \( S^2 \) represents the sample variance, which is an unbiased estimator of the population variance. It is defined as:
\[
S^2 = \frac{1}{n-1} \sum_{i=1}^{n} (X_i - \bar{X})^2
\]
where \( X_1, X_2, \ldots, X_n \) are independent and identically
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