propodds {powertools} | R Documentation |
Power calculations for ordinal categorical variable under proportional odds assumption
Description
Performs power and sample size calculation for a comparison of two groups on an ordinal categorical response variable. Assumes that response probabilities follow the proportional odds assumption. Can solve for power, n1, n.ratio and alpha.
Usage
propodds(pC, OR, n1, n.ratio = 1, alpha = 0.05, power = NULL, v = FALSE)
Arguments
pC |
Vector of response probabilities in control group (group 1). Must sum to 1. Categories are ordered from best to worst. |
OR |
Odds ratio when the alternative is true. Must be greater than 1. |
n1 |
Sample size for group 1 (control group). |
n.ratio |
The ratio n2/n1 between the sample sizes of two groups; defaults to 1 (equal group sizes). |
alpha |
The significance level (type 1 error rate); defaults to 0.05. |
power |
The specified level of power; defaults to 0.8. |
v |
Either TRUE for verbose output or FALSE (default) to output computed argument only. |
Details
Whitehead J. (1993) Sample size calculations for ordered categorical data. Statistics in Medicine, 12(24):2257–2271
Value
A list of the arguments (including the computed one).
Examples
library(Hmisc)
pC <- c(0.2, 0.5, 0.2, 0.1)
propodds(pC = pC, OR = 2.5, n1 = 65, n.ratio = 1, alpha = 0.05)