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.
Ensure that mtcars
has already been loaded into a DataFrame 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.
Perform the following steps:
- First we plot the two boxplots of factor gears regarding
mpg
, with the plot separated from the transmission type:
> par(mfrow=c(1,2)) > boxplot (mtcars$mpg~mtcars$gear,subset=(mtcars$am==0),xlab='gear' , ylab = "mpg",main='automatic') > boxplot (mtcars$mpg~mtcars$gear,subset=(mtcars$am==1),xlab='gear', ylab = "mpg", main='manual')
The boxplots of mpg by the gear group and the transmission type
- Also, you may produce...