Pairwise Mood's median tests with matrix output

Conducts pairwise Mood's median tests across groups.

Usage

pairwiseMedianMatrix(
  formula = NULL,
  data = NULL,
  x = NULL,
  g = NULL,
  digits = 4,
  method = "fdr",
  ...
)

Arguments

formula: A formula indicating the measurement variable and the grouping variable. e.g. y ~ group.
data: The data frame to use.
x: The response variable as a vector.
g: The grouping variable as a vector.
digits: The number of significant digits to round output.
method: The p-value adjustment method to use for multiple tests. See stats::p.adjust.
...: Additional arguments passed to coin::median_test.

Value

A list consisting of: a matrix of p-values; the p-value adjustment method; a matrix of adjusted p-values.

Details

The input should include either formula and data; or x, and g.

Mood's median test compares medians among two or more groups. See https://rcompanion.org/handbook/F_09.html for futher discussion of this test.

The pairwiseMedianMatrix function can be used as a post-hoc method following an omnibus Mood's median test. It passes the data for pairwise groups to coin::median_test.

The matrix output can be converted to a compact letter display, as in the example.

Note

The parsing of the formula is simplistic. The first variable on the left side is used as the measurement variable. The first variable on the right side is used for the grouping variable.

References

https://rcompanion.org/handbook/F_09.html

Author

Salvatore Mangiafico, mangiafico@njaes.rutgers.edu

Examples

data(PoohPiglet)
PoohPiglet$Speaker = factor(PoohPiglet$Speaker,
                          levels = c("Pooh", "Tigger", "Piglet"))
PT = pairwiseMedianMatrix(Likert ~ Speaker,
                          data   = PoohPiglet,
                          exact  = NULL,
                          method = "fdr")$Adjusted
PT                           
#>            Pooh   Tigger   Piglet
#> Pooh   1.000000 0.614700 0.001465
#> Tigger 0.614700 1.000000 0.003247
#> Piglet 0.001465 0.003247 1.000000
library(multcompView)
multcompLetters(PT,
                compare="<",
                threshold=0.05,
                Letters=letters)                    
#>   Pooh Tigger Piglet 
#>    "a"    "a"    "b"