prec_meandiff {presize}

Sample size or precision for a mean difference

Description

prec_meandiff returns the sample size or the precision for the provided mean difference and standard deviations. For paired differences, use prec_mean, as it is equivalent to a simple mean.

Usage

prec_meandiff(
  delta,
  sd1,
  sd2 = sd1,
  n1 = NULL,
  r = 1,
  conf.width = NULL,
  conf.level = 0.95,
  variance = c("equal", "unequal"),
  ...
)

Arguments

delta

difference in means between the two groups.

sd1

standard deviation in group 1.

sd2

standard deviation in group 2.

n1

number of patients in group 1.

r

allocation ratio (relative size of group 2 and group 1 (n2 / n1)).

conf.width

precision (the full width of the confidence interval).

conf.level

confidence level.

variance

equal (default) or unequal variance.

...

other options to uniroot (e.g. tol)

Details

Exactly one of the parameters n or conf.width must be passed as NULL, and that parameter is determined from the other.

Value

Object of class "presize", a list of arguments (including the computed one) augmented with method and note elements.

Examples

# mean difference of 5, SD of 2.5, CI width with 20 participants assuming equal variances
prec_meandiff(delta = 5, sd1 = 2.5, n1 = 20, var = "equal")
# mean difference of 5, SD of 2.5, number of participants for a CI width of 3,
#  assuming equal variances
prec_meandiff(delta = 5, sd1 = 2.5, conf.width = 3, var = "equal")