size.ci.median {statpsych} | R Documentation |
Sample size for a median confidence interval
Description
Computes the sample size required to estimate a population median with desired confidence interval precision. Set the variance planning value to the largest value within a plausible range for a conservatively large sample size. The sample size requirement depends on the shape of the distribution. Select one of the four distribution options (Normal, Logistic, Laplace, Exponential) that approximates the most likely distribution shape in the planned study. Select the Normal distribution for a conservatively large sample size requirement.
Usage
size.ci.median(alpha, var, w, dist)
Arguments
alpha |
alpha level for 1-alpha confidence |
var |
planning value of response variable variance |
w |
desired confidence interval width |
dist |
|
Value
Returns the required sample size
References
Bonett DG, Price RM (2002). “Statistical inference for a linear function of medians: Confidence intervals, hypothesis testing, and sample size requirements.” Psychological Methods, 7(3), 370–383. ISSN 1939-1463, doi:10.1037/1082-989X.7.3.370.
Examples
size.ci.median(.05, 264.4, 10, 1)
# Should return:
# Sample size
# 64
size.ci.median(.05, 264.4, 10, 3)
# Should return:
# Sample size
# 21