Page 316 - Applied Statistics with R
P. 316
316 CHAPTER 14. TRANSFORMATIONS
gala_model = lm(Species ~ Area + Elevation + Nearest + Scruz + Adjacent, data = gala)
plot(fitted(gala_model), resid(gala_model), col = "dodgerblue",
pch = 20, cex = 1.5, xlab = "Fitted", ylab = "Residuals")
abline(h = 0, lty = 2, col = "darkorange", lwd = 2)
150
100
Residuals 50 0
-100
0 100 200 300 400
Fitted
Even though there is not a lot of data for large fitted values, it still seems very
clear that the constant variance assumption is violated.
boxcox(gala_model, lambda = seq(-0.25, 0.75, by = 0.05), plotit = TRUE)
