Page 315 - Applied Statistics with R

14.1. RESPONSE TRANSFORMATION 315

10

5
Residuals 0

-5

6 8 10 12 14 16

Fitted

Looking at a fitted versus residuals plot verifies that there likely are not any
issue with the assumptions of this model, which Breusch-Pagan and Shapiro-
Wilk tests verify.

library(lmtest)
bptest(savings_model)

##
## studentized Breusch-Pagan test
##
## data: savings_model
## BP = 4.9852, df = 4, p-value = 0.2888
shapiro.test(resid(savings_model))

##
## Shapiro-Wilk normality test
##
## data: resid(savings_model)
## W = 0.98698, p-value = 0.8524
Now we will use the gala dataset as an example of using the Box-Cox method
to justify a transformation other than log. We fit an additive multiple regres-
sion model with Species as the response and most of the other variables as
predictors.