compare.2.vectors {afex} | R Documentation

## Compare two vectors using various tests.

### Description

Compares two vectors `x` and `y` using t-test, Welch-test (also known as Satterthwaite), Wilcoxon-test, and a permutation test implemented in coin.

### Usage

    compare.2.vectors(x, y, paired = FALSE, na.rm = FALSE,
         tests = c("parametric", "nonparametric"), coin = TRUE,
         alternative = "two.sided",
         perm.distribution = approximate(100000),
         wilcox.exact = NULL, wilcox.correct = TRUE)

### Arguments

`x` | a (non-empty) numeric vector of data values.
`y` | a (non-empty) numeric vector of data values.
`paired` | a logical whether the data is paired. Default is `FALSE`.
`na.rm` | logical. Should `NA` be removed? Default is `FALSE`.
`tests` | Which tests to report, parametric or nonparamteric? The default `c("parametric", "nonparametric")` reports both. See details. (Arguments may be abbreviated).
`coin` | logical or character. Should (permutation) tests from the coin package be reported? Default is `TRUE` corresponding to all implemented tests. `FALSE` calculates no tests from coin. A character vector may include any of the following (potentially abbreviated) implemented tests (see also Details): `c("permutation", "Wilcoxon", "median")`
`alternative` | a character, the alternative hypothesis must be one of `"two.sided"` (default), `"greater"` or `"less"`. You can specify just the initial letter, will be passed to all functions.
`perm.distribution` | `distribution` argument to coin, see `NullDistribution` or , `IndependenceTest`. Defaults to `approximate(100000)` indicating an approximation of the excat conditional distribution with 100.000 Monte Carlo samples. One can use `"exact"` for small samples and if `paired = FALSE`.
`wilcox.exact` | `exact` argument to `wilcox.test`.
`wilcox.correct` | `correct` argument to `wilcox.test`.

### Details

The `parametric` tests (currently) only contain the t-test and Welch/Statterwaithe/Smith/unequal variance t-test implemented in `t.test`. The latter one is only displayed if `paired = FALSE`.

The `nonparametric` tests (currently) contain the Wilcoxon test implemented in `wilcox.test` (`stats::Wilcoxon`) and (if `coin = TRUE`) the following tests implemented in coin:

- a `permutation` test `oneway_test` (the only test in this selction not using a rank transformation),

- the `Wilcoxon` test `wilcox_test` (`coin::Wilcoxon`), and

- the `median` test `median_test`.

Note that the two implementations of the Wilcoxon test probably differ. This is due to differences in the calculation of the Null distributions.

### Value

a list with up to two elements (i.e., `paramteric` and/or `nonparamteric`) each containing a `data.frame` with the following columns: `test`, `test.statistic`, `test.value`, `test.df`, `p`.

### Examples

    with(sleep, compare.2.vectors(extra[group == 1], extra[group == 2]))

    # gives:
    ## $parametric
    ##    test test.statistic test.value test.df       p
    ## 1     t              t     -1.861   18.00 0.07919
    ## 2 Welch              t     -1.861   17.78 0.07939
    ##
    ## $nonparametric
    ##              test test.statistic test.value test.df       p
    ## 1 stats::Wilcoxon              W     25.500      NA 0.06933
    ## 2     permutation              Z     -1.751      NA 0.08154
    ## 3  coin::Wilcoxon              Z     -1.854      NA 0.06487
    ## 4          median              Z     -1.744      NA 0.17867

    # compare with:
    with(sleep, compare.2.vectors(extra[group == 1], extra[group == 2], alternative = "less"))

    with(sleep, compare.2.vectors(extra[group == 1], extra[group == 2], alternative = "greater"))

    # doesn't make much sense as the data is not paired, but whatever:
    with(sleep, compare.2.vectors(extra[group == 1], extra[group == 2], paired = TRUE))

    # from ?t.test:
    compare.2.vectors(1:10,y=c(7:20, 200))

[Package afex version 0.18-0 Index]