# 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)`

```
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()
```

*Documentation reproduced from package stats, version 3.3.3, License: Part of R 3.3.3*

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