title: Estimates, power and sample size calculations for two-sample ordinal outcomes under before-after study designs.
abstract: 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.
authors.affiliation: Division of Biometrics, School of Public Health and Cancer Institute of New Jersey, University of Medicine of Dentistry of New Jersey, Suite 2200, Liberty Plaza, 335 George Street, New Brunswick, NJ 08903, USA. ohmanpa@umdnj.edu
authors.forename: Pamela A Ohman
authors.initials: PA
authors.lastname: Strickland
authors.forename: Shou-En
authors.initials: SE
authors.lastname: Lu
mesh_terms: D002986:Clinical Trials as Topic / Q000379:methods / Q000706:statistics & numerical data*; D003627:Data Interpretation, Statistical; D006801:Humans; D016017:Odds Ratio; D018401:Sample Size; D014481:United States