The pooled variance of p samples presumed to have been obtained from p populations having common variance σ2, \documentclass[12pt]{minimal}
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\begin{document}$$S^2_{\rm pooled}$$\end{document} has invariably been adopted as the default estimator for σ2. In this paper, alternative estimators of the common population variance are developed. These estimators are biased and have lower mean-squared error values than \documentclass[12pt]{minimal}
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\begin{document}$$S^2_{\rm pooled}$$\end{document} . The comparative merit of these estimators over the unbiased estimator is explored using relative efficiency (a ratio of mean-squared error values).