posthocTGH: posthocTGH

In userfriendlyscience: Quantitative Analysis Made Accessible

Description

This function is used by the 'oneway' function for oneway analysis of variance in case a user requests post-hoc tests using the Tukey or Games-Howell methods.

Usage

posthocTGH(y, x, method=c("games-howell", "tukey"),
           conf.level = 0.95, digits=2, p.adjust="none",
           formatPvalue = TRUE)

Arguments

y	y has to be a numeric vector.
x	x has to be vector that either is a factor or can be converted into one.
method	Which post-hoc tests to conduct. Valid values are "tukey" and "games-howell".
conf.level	Confidence level of the confidence intervals.
digits	The number of digits to show in the output.
p.adjust	Any valid p.adjust method.
formatPvalue	Whether to format the p values according to APA standards (i.e. replace all values lower than .001 with '<.001'). This only applies to the printing of the object, not to the way the p values are stored in the object.

Value

A list of three elements:

input	List with input arguments
intermediate	List of intermediate objects.
output	List with two objects 'tukey' and 'games.howell', containing the outcomes for the respective post-hoc tests.

Note

This function is based on a file that was once hosted at http://www.psych.yorku.ca/cribbie/6130/games_howell.R, but has been removed since. It was then adjusted for implementation in the userfriendlyscience package. Jeffrey Baggett needed the confidence intervals, and so emailed them, after which his updated function was used. In the meantime, it appears Aaron Schlegel (https://rpubs.com/aaronsc32) independently developed a version with confidence intervals and posted it on RPubs at https://rpubs.com/aaronsc32/games-howell-test.

Also, for some reason, p.adjust can be used to specify additional correction of p values. I'm not sure why I implemented this, but I'm not entirely sure it was a mistake either. Therefore, in userfriendlyscience version 0.6-2, the default of this setting changed from "holm" to "none" (also see https://stats.stackexchange.com/questions/83941/games-howell-post-hoc-test-in-r).

Author(s)

Gjalt-Jorn Peters (Open University of the Netherlands) & Jeff Bagget (University of Wisconsin - La Crosse)

Maintainer: Gjalt-Jorn Peters <[e-mail]>

Examples

### Compute post-hoc statistics using the tukey method
posthocTGH(y=ChickWeight$weight, x=ChickWeight$Diet, method="tukey");
### Compute post-hoc statistics using the games-howell method
posthocTGH(y=ChickWeight$weight, x=ChickWeight$Diet);

Example output

sh: 1: cannot create /dev/null: Permission denied
    n means variances
1 220   103      3210
2 120   123      5128
3 120   143      7489
4 118   135      4737

    diff ci.lo ci.hi    t  df    p p.adjusted
2-1 20.0  -0.3    40 2.54 574  .06        .22
3-1 40.3  20.0    61 5.12 574 <.01       <.01
4-1 32.6  12.2    53 4.12 574 <.01       <.01
3-2 20.3  -2.7    43 2.27 574  .11        .32
4-2 12.6 -10.5    36 1.41 574  .50        .99
4-3 -7.7 -30.8    15 0.86 574  .83        .99
    n means variances
1 220   103      3210
2 120   123      5128
3 120   143      7489
4 118   135      4737

    diff  ci.lo ci.hi    t  df    p p.adjusted
2-1 20.0   0.36    40 2.64 201  .04        .18
3-1 40.3  17.54    63 4.59 176 <.01       <.01
4-1 32.6  13.45    52 4.41 203 <.01       <.01
3-2 20.3  -6.20    47 1.98 230  .20        .59
4-2 12.6 -10.91    36 1.39 236  .51       1.00
4-3 -7.7 -33.90    19 0.76 226  .87       1.00

userfriendlyscience documentation built on May 2, 2019, 1:09 p.m.