rstatix: dunn_test – R documentation

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dunn_test

Dunn's Test of Multiple Comparisons

Description

Performs Dunn's test for pairwise multiple comparisons of the ranked data. The mean rank of the different groups is compared. Used for post-hoc test following Kruskal-Wallis test.

Usage

dunn_test(data, formula, p.adjust.method = "holm", detailed = FALSE)

Arguments

`data`	a data.frame containing the variables in the formula.
`formula`	a formula of the form `x ~ group` where `x` is a numeric variable giving the data values and `group` is a factor with one or multiple levels giving the corresponding groups. For example, `formula = TP53 ~ cancer_group`.
`p.adjust.method`	method to adjust p values for multiple comparisons. Used when pairwise comparisons are performed. Allowed values include "holm", "hochberg", "hommel", "bonferroni", "BH", "BY", "fdr", "none". If you don't want to adjust the p value (not recommended), use p.adjust.method = "none".
`detailed`	logical value. Default is FALSE. If TRUE, a detailed result is shown.

Details

DunnTest performs the post hoc pairwise multiple comparisons procedure appropriate to follow up a Kruskal-Wallis test, which is a non-parametric analog of the one-way ANOVA. The Wilcoxon rank sum test, itself a non-parametric analog of the unpaired t-test, is possibly intuitive, but inappropriate as a post hoc pairwise test, because (1) it fails to retain the dependent ranking that produced the Kruskal-Wallis test statistic, and (2) it does not incorporate the pooled variance estimate implied by the null hypothesis of the Kruskal-Wallis test.

Value

return a data frame with some of the following columns:

.y.: the y (outcome) variable used in the test.
group1,group2: the compared groups in the pairwise tests.
n1,n2: Sample counts.
estimate: mean ranks difference.
estimate1, estimate2: show the mean rank values of the two groups, respectively.
statistic: Test statistic (z-value) used to compute the p-value.
p: p-value.
p.adj: the adjusted p-value.
method: the statistical test used to compare groups.
p.signif, p.adj.signif: the significance level of p-values and adjusted p-values, respectively.

The returned object has an attribute called args, which is a list holding the test arguments.

References

Dunn, O. J. (1964) Multiple comparisons using rank sums Technometrics, 6(3):241-252.

Examples

# Simple test
ToothGrowth %>% dunn_test(len ~ dose)

# Grouped data
ToothGrowth %>%
  group_by(supp) %>%
  dunn_test(len ~ dose)

rstatix

Pipe-Friendly Framework for Basic Statistical Tests

v0.7.0

GPL-2

Authors

Alboukadel Kassambara [aut, cre]

Initial release