mosaic: ttest – R documentation

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ttest

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

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

Project MOSAIC Statistics and Mathematics Teaching Utilities

v1.8.3

GPL (>= 2)

Authors

Randall Pruim [aut, cre], Daniel T. Kaplan [aut], Nicholas J. Horton [aut]

Initial release