What is missing from this comparison of the two groups?

^{3}

# Comparing Several Groups Using Regression

The connection between the pooled two-sample `t`-test and simple regression hints that we can use multiple regression to compare the means of several groups. Simply add more dummy variables.

For the wheat trials, define dummy variables for the other varieties:

$$\begin{array}{lll}\hfill D\left(\text{Hatcher}\right)& =\hfill & 1\text{if}\text{plot}\text{grows}\text{variety}\text{Hatcher}\text{and}0\text{otherwise}.\hfill \\ \hfill D\left(\text{NuHills}\right)& =\hfill & 1\text{if}\text{plot}\text{grows}\text{variety}\text{NuHills}\text{and}0\text{otherwise}.\hfill \\ \hfill \text{D}\left(\text{Ripper}\right)& =\hfill & 1\text{if}\hfill \end{array}$$

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