vis_group_normality: Visualisation of the normality assumption for Welch...

In visStatistics: Automated Selection and Visualisation of Statistical Hypothesis Tests

Visualisation of the normality assumption for Welch ANOVA/t-test

Description

vis_group_normality checks for normality of each group separately using the Shapiro-Wilk and Anderson-Darling tests. The null hypothesis is that each group is normally distributed. The function generates histograms with normal distribution overlays and Q-Q plots to visually assess normality. The layout is always 2 rows × k columns (histograms on top, Q-Q plots on bottom).

Usage

vis_group_normality(
  samples,
  groups,
  conf.level = 0.95,
  samplename = "",
  groupname = "",
  cex = 1
)

Arguments

samples	Numeric vector; the dependent variable.
groups	Factor or vector; the grouping variable (2 to 8 groups for visual display).
conf.level	Numeric; confidence level (default: 0.95). Used to determine alpha = 1 - conf.level for normality test interpretation.
samplename	Character; label for the y-axis (default: "").
groupname	Character; label for the x-axis (default: "").
cex	Numeric; scaling factor for plot text and symbols (default: 1).

Details

Layout is always 2 rows × k columns:

• Top row: Histograms with normal overlay for each group

• Bottom row: Q-Q plots for each group

For more than 8 groups, a tabular summary is provided instead of plots.

Value

A list containing:

shapiro_tests

List of Shapiro-Wilk test results for each group

ad_tests

List of Anderson-Darling test results for each group

n_groups

Number of groups

group_names

Names of the groups

Examples

# Two groups (like t-test)
vis_group_normality(ToothGrowth$len, ToothGrowth$supp)

# Three groups
ToothGrowth$dose <- as.factor(ToothGrowth$dose)
vis_group_normality(ToothGrowth$len, ToothGrowth$dose)

visStatistics documentation built on May 13, 2026, 1:08 a.m.