r2spss (version 0.3.2)

t_test: t Tests

Description

Perform a one-sample t test, a paired-sample t test or an independent-samples t test on variables of a data set. The output is printed as a LaTeX table that mimics the look of SPSS output.

Usage

t_test(data, variables, group = NULL, mu = 0, conf.level = 0.95)
# S3 method for t_test_SPSS
to_SPSS(
  object,
  statistics = c("test", "statistics"),
  version = r2spss_options$get("version"),
  digits = 3,
  ...
)
# S3 method for t_test_SPSS
print(
  x,
  statistics = c("statistics", "test"),
  version = r2spss_options$get("version"),
  digits = 3,
  ...
)
tTest(data, variables, group = NULL, mu = 0, conf.level = 0.95)

Arguments

data

a data frame containing the variables.

variables

a character vector specifying numeric variable(s) to be used for testing the mean(s). If group is NULL, a one-sample t test is performed if only one variable is specified, and a paired-sample t test is performed if two variables are specified. If a grouping variable is specified in group, an independent-samples t-test is performed and this should be a character string specifying the numeric variable of interest.

group

a character string specifying a grouping variable for an independent-samples t-test, or NULL.

mu

a number indicating the true value of the mean for a one-sample t test.

conf.level

a number between 0 and 1 giving the confidence level of the confidence interval.

object, x

an object of class "t_test_SPSS" as returned by function t_test.

statistics

a character string or vector specifying which SPSS tables to produce. Available options are "statistics" for descriptive statistics and "test" for test results. For the to_SPSS method, only one option is allowed (the default is the table of test results), but the print method allows several options (the default is to print all tables).

version

a character string specifying whether the table should mimic the content and look of recent SPSS versions ("modern") or older versions (<24; "legacy"). The main differences in terms of content are that recent SPSS versions show a one-sided p-value in addition to the two-sided p-value, and that small p-values are displayed differently. For the paired-sample test, recent versions of SPSS also display a label Pair 1 for the selected pair of variables.

digits

an integer giving the number of digits after the comma to be printed in the SPSS tables.

…

additional arguments to be passed down to format_SPSS.

Value

An object of class "t_test_SPSS" with the following components:

statistics

a data frame containing the relevant descriptive statistics.

test

an object of class "htest" as returned by t.test (only one-sample and paired-sample tests).

variables

a character vector containing the name(s) of the relevant numeric variable(s).

n

an integer giving the number of observations (only paired-sample test).

levene

an object as returned by leveneTest (only independent-samples test).

pooled

an object of class "htest" as returned by t.test assuming equal variances (only independent-samples test).

satterthwaite

an object of class "htest" as returned by t.test not assuming equal variance (only independent-samples test).

group

a character string containing the name of the grouping variable (only independent-samples test).

type

a character string giving the type of t test performed ("one-sample", "paired", or "independent").

The to_SPSS method returns an object of class "SPSS_table" which contains all relevant information in the required format to produce the LaTeX table. See to_latex for possible components and how to further customize the LaTeX table based on the returned object.

The print method produces a LaTeX table that mimics the look of SPSS output.

Details

The print method first calls the to_SPSS method followed by to_latex. Further customization can be done by calling those two functions separately, and modifying the object returned by to_SPSS.

Examples

# NOT RUN {
## one-sample and paired-sample t test

# load data
data("Exams")

# test whether the average grade on the resit
# differs from 5.5 (minimum passing grade)
t_test(Exams, "Resit", mu = 5.5)

# test whether average grades differ between the
# regular exam and the resit
t_test(Exams, c("Resit", "Regular"))


## independent-samples t test

# load data
data("Eredivisie")
# log-transform market values
Eredivisie$logMarketValue <- log(Eredivisie$MarketValue)

# test whether average log market values differ between
# Dutch and foreign players
t_test(Eredivisie, "logMarketValue", group = "Foreign")

# }