confintr (version 1.0.0)

ci_mean_diff: 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. The default bootstrap type is "stud" (bootstrap t) as it has a stable variance estimator (see Efron, p. 188). Resampling is done within sample. If 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".

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,
  ...
)

Value

An object of class "cint" containing these components:

• parameter: Parameter specification.

• interval: CI for the parameter.

• estimate: Parameter estimate.

• probs: Lower and upper probabilities.

• type: Type of interval.

• info: Additional description.

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 ("stud", "bca", "perc", "norm", "basic"). 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().

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