REGULAR ARTICLE
A SAS macro for generating letter displays of pairwise mean comparisons
Commun. Biometry Crop Sci. (2012) 7 (1), 4-13.
ABSTRACT
Data from many experiments are routinely subjected to analysis of
variance, followed by a multiple comparison of means. A popular way
to present the result of mean comparisons is by attaching super-
scripted letters to the means, with a common letter on two means
indicating that they are not significantly different. When the
standard error of a difference is not constant, the algorithm
traditionally used for generating such displays may fail to
represent all significant differences. This paper reports on a so-called
insert-and-absorb algorithm that is guaranteed to always truthfully
represent all significant differences. This algorithm was
implemented in a SAS macro %MULT. Its usage is illustrated using three
examples.
Key Words: multiple comparison; insert-and-absorb algorithm; lines display; letter display; compact
letter display; mixed model; generalized linear mixed model; standard error of a difference; analysis of
variance; %MULT macro.
