ttest: Student's t-Test

In mosaic: Project MOSAIC Statistics and Mathematics Teaching Utilities

Student's t-Test

Description

Performs one and two sample t-tests. The mosaic t.test provides wrapper functions around the function of the same name in stats. These wrappers provide an extended interface that allows for a more systematic use of the formula interface.

Usage

t_test(x, ...)

t.test(x, ...)

## S3 method for class 'formula'
t_test(formula, data, ..., groups = NULL)

## Default S3 method:
t_test(
  x,
  y = NULL,
  alternative = c("two.sided", "less", "greater"),
  mu = 0,
  paired = FALSE,
  var.equal = FALSE,
  conf.level = 0.95,
  ...
)

Arguments

x	a (non-empty) numeric vector of data values.
...	further arguments to be passed to or from methods.
formula	a formula of the form lhs ~ rhs where lhs is a numeric variable giving the data values and rhs either 1 for a one-sample or paired test or a factor with two levels giving the corresponding groups. If lhs is of class "Pair" and rhs is 1, a paired test is done
data	an optional matrix or data frame (or similar: see model.frame) containing the variables in the formula formula. By default the variables are taken from environment(formula).
groups	When x is a formula, groups can be used to compare groups: ⁠x = ~ var, groups = g⁠ is equivalent to x = var ~ g. See the examples.
y	an optional (non-empty) numeric vector of data values.
alternative	a character string specifying the alternative hypothesis, must be one of "two.sided" (default), "greater" or "less". You can specify just the initial letter.
mu	a number indicating the true value of the mean (or difference in means if you are performing a two sample test).
paired	a logical indicating whether you want a paired t-test.
var.equal	a logical variable indicating whether to treat the two variances as being equal. If TRUE then the pooled variance is used to estimate the variance otherwise the Welch (or Satterthwaite) approximation to the degrees of freedom is used.
conf.level	confidence level of the interval.

Details

This is a wrapper around stats::t.test() from the stats package to extend the functionality of the formula interface. In particular, one can now use the formula interface for a 1-sample t-test. Before, the formula interface was only permitted for a 2-sample test. The type of formula that can be used for the 2-sample test has also be broadened. See the examples.

Value

an object of class htest

See Also

prop.test(), binom.test(), stats::t.test()

Examples

  t.test(HELPrct$age)
  # We can now do this with a formula
  t.test(~ age, data = HELPrct)
  # data = can be omitted, but it is better to use it
  t.test(~ age, HELPrct)
  # the original 2-sample formula
  t.test(age ~ sex, data = HELPrct)
  # alternative 2-sample formulas
  t.test(~ age | sex, data = HELPrct)
  t.test(~ age, groups = sex, data = HELPrct)
  # 2-sample t from vectors
  with(HELPrct, t.test(age[sex == "male"], age[sex == "female"]))
  # just the means
  mean(age ~ sex, data = HELPrct)

mosaic documentation built on May 29, 2024, 5:27 a.m.