cld.emmGrid: Compact letter displays

Description

A method for multcomp::cld() is provided for users desiring to produce compact-letter displays (CLDs). This method uses the Piepho (2004) algorithm (as implemented in the multcompView package) to generate a compact letter display of all pairwise comparisons of estimated marginal 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.

Usage

# S3 method for emmGrid
cld(object, details = FALSE, sort = TRUE, by,
  alpha = 0.05, Letters = c("1234567890", LETTERS, letters),
  reversed = decreasing, decreasing = FALSE, signif.sets = FALSE,
  delta = 0, ...)
# S3 method for emm_list
cld(object, ..., which = 1)

Value

A summary_emm object showing the estimated marginal means plus an additional column labeled .group (when signif.sets = FALSE), .signif.set (when signif.sets = TRUE), or .equiv.set

(when delta > 0).

Arguments

object: An object of class emmGrid
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.
by: 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, decreasing: Logical value (passed to multcompView::multcompLetters.) If TRUE, the order of use of the letters is reversed. Either reversed or decreasing may be specified, thus providing compatibility with both multcompView::multcompLetters(..., reversed, ...) and multcomp::cld(..., decreasing, ...). In addition, if both sort and reversed are TRUE, the sort order of results is reversed.
signif.sets: Logical value. If FALSE (and delta = 0), a ‘traditional’ compact-letter display is constructed with groupings representing sets of estimates that are not statistically different. If TRUE, the criteria are reversed so that two estimates sharing the same symbol test as significantly different. See also delta.
delta: Numeric value passed to test.emmGrid. If this is positive, it is used as an equivalence threshold in the TOST procedure for two-sided equivalence testing. In the resulting compact letter display, two estimates share the same grouping letter only if they are found to be statistically equivalent -- that is, groupings reflect actual findings of equivalence rather than failure to find a significant difference. When delta is nonzero, signif.sets is ignored.
...: Arguments passed to contrast (for example, an adjust method)
which: Which element of the emm_list object to process (If length exceeds one, only the first one is used)

References

Piepho, Hans-Peter (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

if(requireNamespace("multcomp"))
    emm_example("cld-multcomp")
    # Use emm_example("cld-multcomp", list = TRUE) # to just list the code

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