pairwise.t.test
Pairwise t tests
Calculate pairwise comparisons between group levels with corrections for multiple testing
- Keywords
- htest
Usage
pairwise.t.test(x, g, p.adjust.method = p.adjust.methods,
pool.sd = !paired, paired = FALSE,
alternative = c("two.sided", "less", "greater"),
…)
Arguments
- x
response vector.
- g
grouping vector or factor.
- p.adjust.method
Method for adjusting p values (see
p.adjust
).- pool.sd
switch to allow/disallow the use of a pooled SD
- paired
a logical indicating whether you want paired t-tests.
- alternative
a character string specifying the alternative hypothesis, must be one of
"two.sided"
(default),"greater"
or"less"
. Can be abbreviated.- …
additional arguments to pass to
t.test
.
Details
The pool.sd
switch calculates a common SD for all
groups and uses that for all comparisons (this can be useful if some
groups are small). This method does not actually call t.test
,
so extra arguments are ignored. Pooling does not generalize to paired tests
so pool.sd
and paired
cannot both be TRUE
.
Only the lower triangle of the matrix of possible comparisons is being
calculated, so setting alternative
to anything other than
"two.sided"
requires that the levels of g
are ordered
sensibly.
Value
Object of class "pairwise.htest"
See Also
Examples
library(stats)
# NOT RUN {
attach(airquality)
Month <- factor(Month, labels = month.abb[5:9])
pairwise.t.test(Ozone, Month)
pairwise.t.test(Ozone, Month, p.adj = "bonf")
pairwise.t.test(Ozone, Month, pool.sd = FALSE)
detach()
# }