Check model for (non-)normality of residuals.

check_normality(x, ...)

# S3 method for merMod
check_normality(x, effects = c("fixed", "random"), ...)

Arguments

x

A model object.

...

Currently not used.

effects

Should normality for residuals ("fixed") or random effects ("random") be tested? Only applies to mixed-effects models. May be abbreviated.

Value

Invisibly returns the p-value of the test statistics. A p-value < 0.05 indicates a significant deviation from normal distribution

Details

check_normality() calls stats::shapiro.test and checks the standardized residuals (or Studentized residuals for mixed models) for normal distribution. Note that this formal test almost always yields significant results for the distribution of residuals and visual inspection (e.g. Q-Q plots) are preferable.

Note

For mixed-effects models, studentized residuals, and not standardized residuals, are used for the test. There is also a plot()-method implemented in the see-package.

Examples

m <<- lm(mpg ~ wt + cyl + gear + disp, data = mtcars)
check_normality(m)
#> OK: residuals appear as normally distributed (p = 0.230).
#> 

# plot results
if (require("see")) {
  x <- check_normality(m)
  plot(x)
}
#> OK: residuals appear as normally distributed (p = 0.230).
#> 

if (FALSE) {
# QQ-plot
plot(check_normality(m), type = "qq")

# PP-plot
plot(check_normality(m), type = "pp")
}