R: Pairwise t tests

pairwise.t.test {stats} | R Documentation

## Pairwise t tests

### Description

Calculate pairwise comparisons between group levels with corrections for multiple testing

### 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"`.
`...` | additional arguments to pass to `t.test`.

### Details

The `pool.SD` switch calculates a common SD for all groups and used 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

`t.test`, `p.adjust`

### Examples

    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()

[Package stats version 2.8.1 Index]