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.

- 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.

- ...
Any additional arguments are passed on to the

`print`

function.

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.

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).

```
### Compute post-hoc statistics using the tukey method
posthocTGH(y=ChickWeight$weight, x=ChickWeight$Diet, method="tukey");
#> 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
#> 2-1 20.0 -0.3 40 2.54 574 .06
#> 3-1 40.3 20.0 61 5.12 574 <.01
#> 4-1 32.6 12.2 53 4.12 574 <.01
#> 3-2 20.3 -2.7 43 2.27 574 .11
#> 4-2 12.6 -10.5 36 1.41 574 .5
#> 4-3 -7.7 -30.8 15 0.86 574 .83
### Compute post-hoc statistics using the games-howell method
posthocTGH(y=ChickWeight$weight, x=ChickWeight$Diet);
#> 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
#> 2-1 20.0 0.36 40 2.64 201 .04
#> 3-1 40.3 17.54 63 4.59 176 <.01
#> 4-1 32.6 13.45 52 4.41 203 <.01
#> 3-2 20.3 -6.20 47 1.98 230 .2
#> 4-2 12.6 -10.91 36 1.39 236 .51
#> 4-3 -7.7 -33.90 19 0.76 226 .87
```