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Estimates, power and sample size calculations for two‐sample ordinal outcomes under before–after study designs
Author(s) -
Strickland Pamela A. Ohman,
Lu ShouEn
Publication year - 2003
Publication title -
statistics in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.996
H-Index - 183
eISSN - 1097-0258
pISSN - 0277-6715
DOI - 10.1002/sim.1383
Subject(s) - odds , ordinal data , statistics , sample size determination , odds ratio , ordinal regression , mathematics , sample (material) , random effects model , outcome (game theory) , ordered logit , econometrics , medicine , meta analysis , logistic regression , physics , mathematical economics , thermodynamics
Sample size calculations are given for comparing two groups of subjects, typically referring to active and non‐active intervention groups, on an ordinal outcome in experiments where the subjects are measured before and after intervention. These calculations apply to log‐odds models with random intercepts, treatment, time and treatment‐by‐time interaction terms, the latter being the term of interest. The assumed forms of the odds ratios are flexible, allowing for proportional odds, adjacent categories, or other conditional models for ordinal responses. Simulations studies show that, for given sample sizes, the nominal and actual powers of the proposed test are similar. Copyright © 2003 John Wiley & Sons, Ltd.