Casella Berger: Why is distribution of F-statistic in ANOVA not T^2

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SUMMARY

The discussion centers on Theorem 11.2.8 from Casella & Berger, which defines the ANOVA statistic as the supremum of the T^2 statistic. It establishes that the distribution of the F-statistic in ANOVA follows an F(k-1, n-k) distribution rather than a T^2 distribution, except in the case of two groups where F equals T^2. Key variables include the pooled sample variance (S^2_p), number of observations (n_i), treatment means (θ_i), and overall sample mean (Ȳ). This distinction is crucial for understanding the statistical properties of ANOVA.

PREREQUISITES
  • Understanding of ANOVA (Analysis of Variance) principles
  • Familiarity with T^2 and F distributions
  • Knowledge of pooled sample variance (S^2_p)
  • Basic statistical notation and summation concepts
NEXT STEPS
  • Study the derivation of the F-distribution in ANOVA contexts
  • Explore the implications of the T^2 distribution in hypothesis testing
  • Learn about the conditions under which F = T^2 in two-group scenarios
  • Investigate the role of sample size (n) in the behavior of F and T^2 distributions
USEFUL FOR

Statisticians, data analysts, and researchers involved in experimental design and hypothesis testing will benefit from this discussion, particularly those focusing on ANOVA methodologies and their statistical foundations.

shaikh22ammar
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Theorem 11.2.8 in Casella & Berger defines the ANOVA statistic as a maxima of T^2 statistic as:
<br /> \sup_{\sum a_i = 0} T_a^2 = \sup_{\sum a_i = 0} \left( <br /> \left( S^2_p \sum a_i^2 / n_i \right)^{-1/2} \left( \sum a_i \bar Y_{i \cdot} - \sum a_i \theta_i\right)<br /> \right)^2 = \left( S^2_p \right)^{-1} \sum n_i \left( \bar Y_{i \cdot} - \bar{\bar Y} - \theta_i + \bar{\theta} \right)^2<br />
where all the summations are from 1 to k the no. of treatments and S^2_p, n_i, \theta_i, \bar Y_{i \cdot} are the pooled sample variance, no. of observations of treatment i, its mean, and sample mean respectively. The term inside the square between equals signs follows t distribution but for whatever reason the supremum of the square follows (k-1) F(k-1, n-k), as opposed to t^2.
 
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$$F = t^2$$
only when there are two groups.
 

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