modelcheck: Model checking plots

In s20x: Functions for University of Auckland Course STATS 201/208 Data Analysis

Model checking plots

Description

Draw the teaching diagnostic plots used by older 's20x' workflows. 'modelcheck()' is retained as an exported compatibility helper for model checking, while newer teaching material may use focused diagnostic helpers such as [eovcheck()], [normcheck()], and [cooks20x()] directly.

Usage

modelcheck(x, ...)

## S3 method for class 'lm'
modelcheck(
  x,
  which = 1:3,
  mar = c(3, 4, 1.5, 4),
  engine = c("base", "ggplot2"),
  ...
)

Arguments

x	The fitted model.
which	The plot(s) to be drawn. Residuals versus fitted values (which = 1), histogram and Q-Q plot of residuals (which = 2), and Cook's distance plot (which = 3).
mar	Margins applied to each selected plot. Ignored by the ggplot2 engine.
engine	plotting engine to use. The default, "base", preserves the original base graphics output. Use "ggplot2" for optional ggplot2 objects.
...	any other arguments to pass to plot for the base engine. Extra arguments are currently ignored by the ggplot2 engine.

Details

The default base graphics engine preserves the original teaching plots and draws directly on the active graphics device. The optional ggplot2 engine is intended for users who want reusable plot objects for reports or further customisation; it requires ggplot2 to be installed and returns ggplot objects instead of drawing base graphics side effects.

Value

Draws diagnostic plots for teaching model checking when using the base engine. With engine = "ggplot2", returns a ggplot object for a single selected plot, or a named list of ggplot objects for multiple selected plots.

Examples

data(peru.df)
lmFit = lm(BP ~ weight, data = peru.df)

# Plot residuals versus fitted values only
modelcheck(lmFit, 1)

# Plot residuals versus fitted values, histogram, and Q-Q plot
modelcheck(lmFit, 1:2)

# Plot all diagnostics
modelcheck(lmFit)

# Optional ggplot2 engine for reusable plot objects
if (requireNamespace("ggplot2", quietly = TRUE)) {
  diagnosticPlots = modelcheck(lmFit, engine = "ggplot2")
  names(diagnosticPlots)

  modelcheck(lmFit, which = 1, engine = "ggplot2")
  modelcheck(lmFit, which = 2, engine = "ggplot2")
  modelcheck(lmFit, which = 3, engine = "ggplot2")
}

s20x documentation built on July 1, 2026, 9:06 a.m.