ntbf01: Sample size calculations for \(t\)-test Bayes factor

Description

This function computes the required sample size to obtain a \(t\)-test Bayes factor (tbf01) more extreme than a threshold k with a specified target power.

Usage

ntbf01(
  k,
  power,
  null = 0,
  plocation = 0,
  pscale = 1/sqrt(2),
  pdf = 1,
  type = c("two.sample", "one.sample", "paired"),
  alternative = c("two.sided", "less", "greater"),
  dpm = plocation,
  dpsd = pscale,
  lower.tail = TRUE,
  integer = TRUE,
  nrange = c(2, 10^4),
  ...
)

Value

The required sample size to achieve the specified power

Arguments

k: Bayes factor threshold
power: Target power
null: Standardized mean difference under the point null hypothesis. Defaults to 0
plocation: \(t\) prior location. Defaults to 0
pscale: \(t\) prior scale. Defaults to 1/sqrt(2)
pdf: \(t\) prior degrees of freedom. Defaults to 1 (a Cauchy prior)
type: Type of \(t\)-test. Can be "two.sample" (default), "one.sample", or "paired"
alternative: Direction of the test. Can be either "two.sided" (default), "less", or "greater". The latter two truncate the analysis prior to negative and positive effects, respectively. If set to "less" or "greater", the power is only computed based on data with effect estimates in the direction of the alternative
dpm: Mean of the normal design prior assigned to the standardized mean difference. Defaults to the analysis prior location
dpsd: Standard deviation of the normal design prior assigned to the standardized mean difference. Set to 0 to obtain a point prior at the design prior mean. Defaults to the analysis prior scale
lower.tail: Logical indicating whether Pr(\(\mathrm{BF}_{01}\) \(\leq\) k) (TRUE) or Pr(\(\mathrm{BF}_{01}\) \(>\) k) (FALSE) should be computed. Defaults to TRUE
integer: Logical indicating whether only integer valued sample sizes should be returned. If TRUE the required sample size is rounded to the next larger integer. Defaults to TRUE
nrange: Sample size search range over which numerical search is performed. Defaults to c(2, 10^4)
...: Other arguments passed to stats::uniroot

Author

Samuel Pawel

Examples

Run this code

 ## example from Schönbrodt and Wagenmakers (2018, p.135)
 ntbf01(k = 1/6, power = 0.95, dpm = 0.5, dpsd = 0, alternative = "greater")
 ntbf01(k = 1/6, power = 0.95, dpm = 0.5, dpsd = 0.1, alternative = "greater")
 ntbf01(k = 6, power = 0.95, dpm = 0, dpsd = 0, alternative = "greater",
        lower.tail = FALSE, nrange = c(2, 10000))