Ansari_Bradley_test: Ansari-Bradley Test of Homogeneity of Variances

In varequal: Tests and Measures for Homoscedasticity

Ansari-Bradley Test of Homogeneity of Variances

Description

Performs Ansari-Bradley test to assess the null hypothesis that the variances are equal across all groups (samples) defined by the independent variable.

Usage

Ansari_Bradley_test(
  data,
  formula,
  alpha = 0.05,
  silent = FALSE,
  summary = FALSE,
  misc = FALSE
)

Arguments

data	A data frame containing the variables specified in the formula.
formula	A formula of the form DV ~ IV, where DV is the dependent (response) variable and IV is the independent (grouping) variable.
alpha	A numeric value specifying the significance level. Must be between 0 and 1. Default is 0.05.
silent	A logical value. If FALSE (default), results are printed to the console. If TRUE, no output is printed.
summary	A logical value (default: FALSE). If TRUE, a summary table for the input data is returned.
misc	A logical value. If FALSE (default), only essential parameters are returned. If TRUE, additional auxiliary parameters are included in the output.

Details

This function is based on Conover et al. (1981) and uses an approximate chi-square test. Results may be inaccurate for small total sample sizes (N < 20) or when there are many tied values.

Value

A list containing the test statistics, p-value, degrees of freedom, and optionally a summary table and/or auxiliary parameters, depending on the values of summary and misc.

References

Ansari, A. R., & Bradley, R. A. (1960). Rank-sum tests for dispersions. The Annals of Mathematical Statistics, 31, 1174–1189.

Conover, W. J., Johnson, M. E., & Johnson, M. M. (1981). A comparative study of tests for homogeneity of variances, with applications to the outer continental shelf bidding data. Technometrics, 23, 351–361. https://doi.org/10.1080/00401706.1981.10487680

See Also

stats::ansari.test

Examples

df0 <- CYCB1[[1]]
out <- Ansari_Bradley_test(df0, cells ~ grp)
boxplot(cells ~ grp, df0, horizontal = TRUE)
points(x = df0$cells, y = jitter(as.numeric(df0$grp), amount = 0.15))

varequal documentation built on Sept. 5, 2026, 5:08 p.m.