One advantage to writing a single model that includes all levels of a qualitative variable rather a separate model for each level is that we obtain a pooled estimate of $\sigma ^ { 2 }$ .

Question

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A single model that includes all levels of a qualitative variable allows for the estimation of a common variance ($\sigma^2$) across all levels, providing a pooled estimate.

One Advantage to Writing a Single Model That Includes All σ2\sigma ^ { 2 }σ2

One Advantage to Writing a Single Model That Includes All $\sigma ^ { 2 }$