title: Addressing missing participant outcome data in dental clinical trials.
abstract: Missing outcome data are common in clinical trials and despite a well-designed study protocol, some of the randomized participants may leave the trial early without providing any or all of the data, or may be excluded after randomization. Premature discontinuation causes loss of information, potentially resulting in attrition bias leading to problems during interpretation of trial findings. The causes of information loss in a trial, known as mechanisms of missingness, may influence the credibility of the trial results. Analysis of trials with missing outcome data should ideally be handled with intention to treat (ITT) rather than per protocol (PP) analysis. However, true ITT analysis requires appropriate assumptions and imputation of missing data. Using a worked example from a published dental study, we highlight the key issues associated with missing outcome data in clinical trials, describe the most recognized approaches to handling missing outcome data, and explain the principles of ITT and PP analysis.
authors.affiliation: Institut für Biometrie, Medizinische Hochschule Hannover, Hannover, Germany.
authors.forename: Loukia M
authors.initials: LM
authors.lastname: Spineli
authors.affiliation: Barts and the London School of Medicine and Dentistry, Institute of Dentistry, Queen Mary University, London, United Kingdom.
authors.forename: Padhraig S
authors.initials: PS
authors.lastname: Fleming
authors.affiliation: Department of Orthodontics and Dentofacial Orthopedics, Dental School/Medical Faculty, University of Bern, Switzerland; Private Practice, Corfu, Greece. Electronic address: npandis@yahoo.com.
authors.forename: Nikolaos
authors.initials: N
authors.lastname: Pandis
mesh_terms: D003627:Data Interpretation, Statistical; D018865:Dental Research / Q000379:methods* / Q000706:statistics & numerical data; D006801:Humans; D057194:Intention to Treat Analysis / Q000379:methods*; D017063:Outcome Assessment, Health Care / Q000379:methods / Q000706:statistics & numerical data; D016032:Randomized Controlled Trials as Topic / Q000379:methods* / Q000706:statistics & numerical data*
keywords: Attrition bias; Intention-to-treat analysis; Missing at random; Missing outcome data; Per protocol analysis; Randomized controlled trials