Sample size for a within-subjects mean linear contrast confidence interval

Computes the sample size required to estimate a linear contrast of population means with desired confidence interval precision in a within-subjects design. Set the variance planning value to the largest value within a plausible range for a conservatively large sample size. Set the Pearson correlation planning value to the smallest value within a plausible range for a conservatively large sample size.

For more details, see Section 4.26 of Bonett (2021, Volume 1)

Usage

size.ci.lc.mean.ws(alpha, var, cor, w, q)

Arguments

alpha

alpha level for 1-alpha confidence

var

planning value of average variance of the measurements

cor

planning value of average correlation between measurements

w

desired confidence interval width

q

vector of within-subjects contrast coefficients

Value

Returns the required sample size

References

Bonett DG (2021). Statistical Methods for Psychologists https://dgbonett.sites.ucsc.edu/.

Examples

q <- c(.5, .5, -.5, -.5)
size.ci.lc.mean.ws(.05, 161.9, .77, 4, q)
#>  Sample size
#>           38

# Should return:
# Sample size
#          38