afex: compare.2.vectors – R documentation

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compare.2.vectors

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, 
     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`. If missing, defaults to `coin::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))

afex

Analysis of Factorial Experiments

v0.28-1

GPL (>= 2)

Authors

Henrik Singmann [aut, cre] (<https://orcid.org/0000-0002-4842-3657>), Ben Bolker [aut], Jake Westfall [aut], Frederik Aust [aut] (<https://orcid.org/0000-0003-4900-788X>), Mattan S. Ben-Shachar [aut], Søren Højsgaard [ctb], John Fox [ctb], Michael A. Lawrence [ctb], Ulf Mertens [ctb], Jonathon Love [ctb], Russell Lenth [ctb], Rune Haubo Bojesen Christensen [ctb]

Initial release