CLD: Extract and display information on all pairwise comparisons of least-squares means.

Description

Extract and display information on all pairwise comparisons of least-squares means.

Usage

CLD(object, ...)
# S3 method for emmGrid
CLD(object, details = FALSE, sort = TRUE, by,
  alpha = 0.05, Letters = c("1234567890", LETTERS, letters),
  reversed = FALSE, ...)
# S3 method for emmGrid
cld(object, ...)

Arguments

object

An object of class emmGrid

...

Arguments passed to contrast (for example, an adjust method)

This function uses the Piepho (2004) algorithm (as implemented in the multcompView package) to generate a compact letter display of all pairwise comparisons of least-squares means. The function obtains (possibly adjusted) P values for all pairwise comparisons of means, using the contrast function with method = "pairwise". When a P value exceeds alpha, then the two means have at least one letter in common.

details

Logical value determining whether detailed information on tests of pairwise comparisons is displayed

sort

Logical value determining whether the EMMs are sorted before the comparisons are produced. When TRUE, the results are displayed according to reversed.

Character value giving the name or names of variables by which separate families of comparisons are tested. If NULL, all means are compared. If missing, the object's by.vars setting, if any, is used.

alpha

Numeric value giving the significance level for the comparisons

Letters

Character vector of letters to use in the display. Any strings of length greater than 1 are expanded into individual characters

reversed

Logical value (passed to multcompView::multcompLetters.) If TRUE, the order of use of the letters is reversed. In addition, if both sort and reversed are TRUE, the sort order of results is reversed.

Value

When details == FALSE, an object of class summary.ref_grid (which inherits from data.frame) showing the summary of EMMs with an added column named .groups containing the CLD information. When details == TRUE, a list with the object just described, as well as the summary of the contrast results showing each comparison, its estimate, standard error, t ratio, and adjusted P value.

References

Hans-Peter Piepho (2004) An algorithm for a letter-based representation of all pairwise comparisons, Journal of Computational and Graphical Statistics, 13(2), 456-466.

Examples

Run this code

# NOT RUN {
warp.lm <- lm(breaks ~ wool * tension, data = warpbreaks)
warp.emm <- emmeans(warp.lm, ~ tension | wool)
CLD(warp.emm)                  # implicitly uses by = "wool"
CLD(warp.emm, by = "tension")  # overrides implicit 'by'

# Mimic grouping bars and compare all 6 means
CLD(warp.emm, by = NULL, Letters = "||||||||", alpha = .01)
# }