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

In summary, Theorem 11.2.8 in Casella & Berger defines the ANOVA statistic as a maxima of T^2 statistic. The ANOVA statistic is equal to the supremum of the square of a term, which follows a t distribution. However, when there are more than two groups, the supremum of the square follows a (k-1) F(k-1, n-k) distribution, instead of a t^2 distribution.
  • #1
shaikh22ammar
1
0
Theorem 11.2.8 in Casella & Berger defines the ANOVA statistic as a maxima of [itex] T^2 [/itex] statistic as:
[tex]
\sup_{\sum a_i = 0} T_a^2 = \sup_{\sum a_i = 0} \left(
\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)
\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
[/tex]
where all the summations are from 1 to [itex] k [/itex] the no. of treatments and [itex] S^2_p, n_i, \theta_i, \bar Y_{i \cdot}[/itex] are the pooled sample variance, no. of observations of treatment [itex] i [/itex], 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 [itex] (k-1) F(k-1, n-k)[/itex], as opposed to [itex] t^2 [/itex].
 
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  • #2
$$F = t^2$$
only when there are two groups.
 

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

What is the F-statistic in ANOVA?

The F-statistic in ANOVA (Analysis of Variance) is a ratio that compares the variance between group means to the variance within the groups. It is used to determine whether there are statistically significant differences between the means of different groups in a dataset.

Why is the F-distribution used instead of the T-distribution in ANOVA?

The F-distribution is used in ANOVA because it is derived from the ratio of two independent chi-squared distributions, which is appropriate for comparing variances. The T-distribution, on the other hand, is used for estimating the mean of a normally distributed population when the sample size is small and the population standard deviation is unknown.

What are the assumptions underlying the F-statistic in ANOVA?

The assumptions underlying the F-statistic in ANOVA include the following: (1) the populations from which the samples are drawn must be normally distributed, (2) the samples must be independent, and (3) the variances of the populations must be equal (homogeneity of variance).

How is the F-statistic calculated in ANOVA?

The F-statistic is calculated by dividing the mean square between the groups (MSB) by the mean square within the groups (MSW). MSB is computed as the variance of the group means multiplied by the number of observations per group, while MSW is the average of the variances within each group.

What does it mean if the F-statistic is significantly large?

If the F-statistic is significantly large, it indicates that there is a greater amount of variance between the group means compared to the variance within the groups. This suggests that at least one group mean is different from the others, leading to the rejection of the null hypothesis that all group means are equal.

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