ci_mean_diff: CI for the Population Mean Difference

In confintr: Confidence Intervals

CI for the Population Mean Difference

Description

This function calculates CIs for the population value of mean(x) - mean(y). The default is Student's method with Welch's correction for unequal variances, but also bootstrap CIs are available.

Usage

ci_mean_diff(
  x,
  y,
  probs = c(0.025, 0.975),
  var.equal = FALSE,
  type = c("t", "bootstrap"),
  boot_type = c("stud", "bca", "perc", "norm", "basic"),
  R = 9999L,
  seed = NULL,
  ...
)

Arguments

x	A numeric vector.
y	A numeric vector.
probs	Lower and upper probabilities, by default c(0.025, 0.975).
var.equal	Should the two variances be treated as being equal? The default is FALSE. If TRUE, the pooled variance is used to estimate the variance of the mean difference. Otherweise, Welch's approach is used. This also applies to the "stud" bootstrap.
type	Type of CI. One of "t" (default), or "bootstrap".
boot_type	Type of bootstrap CI. Only used for type = "bootstrap".
R	The number of bootstrap resamples. Only used for type = "bootstrap".
seed	An integer random seed. Only used for type = "bootstrap".
...	Further arguments passed to boot::boot().

Details

The default bootstrap type is "stud" (bootstrap t) as it has a stable variance estimator (see Efron, p. 188). Resampling is done within sample. When boot_type = "stud", the standard error is estimated by Welch's method if var.equal = FALSE (the default), and by pooling otherwise. Thus, var.equal not only has an effect for the classic Student approach (type = "t") but also for boot_type = "stud".

Value

An object of class "cint", see ci_mean() for details.

References

Efron, B. and Tibshirani R. J. (1994). An Introduction to the Bootstrap. Chapman & Hall/CRC.

Examples

x <- 10:30
y <- 1:30
ci_mean_diff(x, y)
t.test(x, y)$conf.int
ci_mean_diff(x, y, type = "bootstrap", R = 999)  # Use larger R

confintr documentation built on June 7, 2023, 6:24 p.m.