Artcat: Sample-size calculation for an ordered categorical outcome. (March 2023)

• Record Type: Journal Article
• Authors: White, Ian R.; Marley-Zagar, Ella; Morris, Tim P.; Parmar, Mahesh K. B.; Royston, Patrick; Babiker, Abdel G.
• Is Part Of: Stata journal. Volume 23:Number 1(2023)
• Page Start: 3
• Page End: 23
• Publication Date: 2023-03
• Subjects: st0700 -- artcat -- sample size -- power -- clinical trial -- randomized controlled trial -- noninferiority trial -- substantial-superiority trial -- categorical variable -- proportional-odds model -- evaluation; Statistics -- Periodicals; Statistics -- Computer programs -- Periodicals; 001.422
• DOI: 10.1177/1536867X231161934
• Languages: English
• ISSNs: 1536-867X

Abstract

We describe a new command, artcat, that calculates sample size or power for a randomized controlled trial or similar experiment with an ordered categorical outcome, where analysis is by the proportional-odds model.artcat implements the method of Whitehead (1993, Statistics in Medicine 12: 2257–2271). We also propose and implement a new method that 1) allows the user to specify a treatment effect that does not obey the proportional-odds assumption, 2) offers greater accuracy for large treatment effects, and 3) allows for noninferiority trials. We illustrate the command and explore the value of an ordered categorical outcome over a binary outcome in various settings. We show by simulation that the methods perform well and that the new method is more accurate than Whitehead's method.