diagnostics
aug_m3 &lt;- augment(m3)

ggplot(aug_m3, aes(x = .fitted, y = .resid)) +
  geom_point() +
  geom_hline(yintercept = 0, linetype = "dashed") +
  labs(x = "Fitted values", y = "Residuals")

ggplot(aug_m3, aes(x = .fitted, y = abs(.resid))) +
  geom_point() +
  geom_hline(yintercept = 0, linetype = "dashed") +
  labs(x = "Fitted values", y = "Absolute value of residuals")

ggplot(aug_m3, aes(x = 1:nrow(aug_m3), y = .resid)) +
  geom_point() +
  geom_hline(yintercept = 0, linetype = "dashed") +
  la