Sample size for a between-subjects standardized linear contrast of means confidence interval

Source: R/statpsych1.R

Computes the sample size per group (assuming equal sample sizes) required to estimate two types of standardized linear contrasts of population means (unweighted average standardizer and single group standardizer) with desired confidence interval precision in a between-subjects design. Set the standardized linear contrast of means to the largest value within a plausible range for a conservatively large sample size.

size.ci.lc.stdmean.bs(alpha, d, w, v)

Arguments

alpha

alpha level for 1-alpha confidence

d

planning value of standardized linear contrast of means

w

desired confidence interval width

v

vector of between-subjects contrast coefficients

Value

Returns the required sample size per group for each standardizer

References

Bonett DG (2009). “Estimating standardized linear contrasts of means with desired precision.” Psychological Methods, 14(1), 1--5. ISSN 1939-1463, doi:10.1037/a0014270 .

Examples

v <- c(.5, .5, -.5, -.5)
size.ci.lc.stdmean.bs(.05, 1, .6, v)
#>                            Sample size per group
#> Unweighted standardizer:                      49
#> Single group standardizer:                    65

# Should return:
#                            Sample size per group
# Unweighted standardizer:                      49
# Single group standardizer:                    65