title: The impact of loss to follow-up on hypothesis tests of the treatment effect for several statistical methods in substance abuse clinical trials.
abstract: "Loss to follow-up" can be substantial in substance abuse clinical trials. When extensive losses to follow-up occur, one must cautiously analyze and interpret the findings of a research study. Aims of this project were to introduce the types of missing data mechanisms and describe several methods for analyzing data with loss to follow-up. Furthermore, a simulation study compared Type I error and power of several methods when missing data amount and mechanism varies. Methods compared were the following: Last observation carried forward (LOCF), multiple imputation (MI), modified stratified summary statistics (SSS), and mixed effects models. Results demonstrated nominal Type I error for all methods; power was high for all methods except LOCF. Mixed effect model, modified SSS, and MI are generally recommended for use; however, many methods require that the data are missing at random or missing completely at random (i.e., "ignorable"). If the missing data are presumed to be nonignorable, a sensitivity analysis is recommended.
authors.affiliation: Department of Biostatistics, Bioinformatics and Epidemiology, Medical University of South Carolina, Charleston, SC 29425, USA. shedden@jhsph.edu
authors.forename: Sarra L
authors.initials: SL
authors.lastname: Hedden
authors.forename: Robert F
authors.initials: RF
authors.lastname: Woolson
authors.forename: Rickey E
authors.initials: RE
authors.lastname: Carter
authors.forename: Yuko
authors.initials: Y
authors.lastname: Palesch
authors.forename: Himanshu P
authors.initials: HP
authors.lastname: Upadhyaya
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Malcolm
mesh_terms: D015982:Bias; D002986:Clinical Trials as Topic / Q000592:standards / Q000706:statistics & numerical data*; D003198:Computer Simulation; D003627:Data Interpretation, Statistical; D005500:Follow-Up Studies; D006801:Humans; D015233:Models, Statistical; D010352:Patient Dropouts / Q000706:statistics & numerical data; D019966:Substance-Related Disorders / Q000534:rehabilitation; D016896:Treatment Outcome