xpssTtest: Performs a T-Test
In translateSPSS2R: Toolset for Translating SPSS-Syntax to R-Code

Description Usage Arguments Details Value Author(s) Examples

R implementation of the SPSS T-TEST function.

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xpssTtest(x, variables = NULL, t_test = "testval", testval = NULL,
  criteria = 0.95, groupvar = NULL, groups = NULL, withvars = NULL,
  paired = FALSE, missing = "analysis")

`x`	a (non-empty) data.frame or input data of class `"xpssFrame"`.
`variables`	atomic character or character vector with the names of the variables.
`t_test`	atomic character definies the type of t-test. Default is `testval`, a one-sample t-test. Optional arguments are `groups` for an independent-sample test and `pairs` for an paires-sample test
`testval`	atomic numeric which indicates the value of mean difference.
`criteria`	atomic numeric which specifies the confidence interval for the mean differences. Default is `"0.95"`, optionally a customized value between 0 and 1 can be used.
`groupvar`	atomic character with the name of the variable which shall be used for grouping.
`groups`	factor variable which specify the variables grouped for an independentsample t-test.
`withvars`	atomic characters or character vector with the name of the paired variables which shall be used for compare the means. Optionally the argument `with` can be chosen to compare the means of 2 pairs.
`paired`	logical. Indicating whether the comparison should be pair based or not.
`missing`	atomic character determines the method which indicates what should happen when the data contains NAs. Default is analysis. Optionally `include` oder `listwise` can be used.

Performs a Student's T-Test. The xpssTtest compares the mean by calculating Students-t of the selected distributions.

It is possible to check the samples.

against a specific value (one-sample) -> testval
in difference of groups (independent-sample)-> groups
in difference of variables (paired-sample) -> pairs

Simple statistics will be printed with every t-test. At the one-sample test, the mean difference will be visualized with the statistics
At the independend-sample test, the mean differnce and ANOVA will be visualized with the statistics
At the paired-sample test, the mean diference and a correlation statistic will be visualizied with the statistics

returns a list depending upon the t-test.

All t-test contain:

	`statistics`	simple statistics.
	`parameter`	degrees of freedom.
	`p.value`	significance level.
	`conf.int`	confidence bound.
	`null.value`	value of null hypothesis.
	`alternative`	value of alternative hypothesis.
	`method`	character string with the name of the t-test.
	`data.name`	name of the data.

The independent t-test includes additonally:

anova anova of the groups.

The paired t-test includes additonally:

corr correlation of the pairs.

Bastian Wiessner

data(fromXPSS)


xpssTtest(fromXPSS,
                   variables = "V7_2",
                   t_test = "testval",
                   testval= 50,
                   criteria = 0.65)

xpssTtest(fromXPSS,
                   t_test = "pairs",
                   variables=c("V5",
                               "V6",
                               "V7_1",
                               "V7_2"),
                   paired = FALSE,
                   missing = "analysis",
                   criteria = 0.85)

xpssTtest(fromXPSS,
                   variables = "V7_2",
                   t_test = "groups",
                   groupvar = "V3",
                   groups = c(1, 2),
                   missing = "analysis",
                   criteria = 0.99)