Page 295 - Applied Statistics with R

13.4. DATA ANALYSIS EXAMPLES 295

mtcars: Fitted versus Residuals

6

4

Residual 2 0

-2

-4

15 20 25

Fitted

The fitted versus residuals plot looks good. We don’t see any obvious pattern,
and the variance looks roughly constant. (Maybe a little larger for large fitted
values, but not enough to worry about.)

bptest(mpg_hp_add)

##
## studentized Breusch-Pagan test
##
## data: mpg_hp_add
## BP = 7.5858, df = 2, p-value = 0.02253

The Breusch-Pagan test verifies this, at least for a small value.

qqnorm(resid(mpg_hp_add), col = "darkgrey")
qqline(resid(mpg_hp_add), col = "dodgerblue", lwd = 2)