title: Analyzing Proportion Scores as Outcomes for Prevention Trials: a Statistical Primer.
abstract: In prevention trials, outcomes of interest frequently include data that are best quantified as proportion scores. In some cases, however, proportion scores may violate the statistical assumptions underlying common analytic methods. In this paper, we provide guidelines for analyzing frequency and proportion data as primary outcomes. We describe standard methods including generalized linear regression models to compare mean proportion scores and examine tools for testing normality and other assumptions for each model. Recommendations are made for instances when the assumptions are not met, including transformations for proportion scores that are non-normal. We also discuss more sophisticated analytical tools to model change in proportion scores over time. The guidelines provide ready-to-use analytical strategies for frequency and proportion data that are commonly encountered in prevention science.
authors.affiliation: Department of Statistics, University of Pittsburgh, Pittsburgh, PA, USA.|Department of Psychiatry, University of Pittsburgh, Pittsburgh, PA, USA.
authors.forename: Kehui
authors.initials: K
authors.lastname: Chen
authors.affiliation: Department of Statistics, University of Pittsburgh, Pittsburgh, PA, USA.|Department of Psychiatry, University of Pittsburgh, Pittsburgh, PA, USA.
authors.forename: Yu
authors.initials: Y
authors.lastname: Cheng
authors.affiliation: Department of Psychiatry, University of Pittsburgh, Pittsburgh, PA, USA.
authors.forename: Olga
authors.initials: O
authors.lastname: Berkout
authors.affiliation: Department of Psychiatry, University of Pittsburgh, Pittsburgh, PA, USA. lindhiemoj@upmc.edu.
authors.forename: Oliver
authors.initials: O
authors.lastname: Lindhiem
mesh_terms: D002986:Clinical Trials as Topic; D006801:Humans; D016014:Linear Models; D017063:Outcome Assessment, Health Care / Q000706:statistics & numerical data*; D011315:Preventive Medicine
keywords: Beta regression; Data transformations; Generalized linear models; Prevention trials; Proportion scores