Performing a two-way ANOVA

A two-way ANOVA can be viewed as the extension of a one-way ANOVA, for the analysis covers more than two categorical variables rather than one. In this recipe, we will discuss how to conduct a two-way ANOVA in R.

Getting ready

Ensure that mtcars has already been loaded into a data frame within an R session. Since the twoway.test, TukeyHSD and interaction.plot functions are originated from the stats package, make sure the library, stats, is loaded.

How to do it...

Perform the following steps:

  1. First we plot the two boxplots of factor gears in regard to mpg, with the plot separated from the transmission type:
    > par(mfrow=c(1,2))
    > boxplot(mtcars$mpg~mtcars$gear,subset=(mtcars$am==0),xlab='gear', ylab = "mpg",main='automatic') ...

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