title: Incomplete quality of life data in randomized trials: missing items.
abstract: Missing data has been a problem in many quality of life studies. This paper focuses upon the issues involved in handling forms which contain one or more missing items, and reviews the alternative procedures. One of the most widely practised approaches is imputation using the mean of all observed items in the same subscale. This, together with the related estimation of the subscale score, is based upon traditional psychometric approaches to scale design and analysis. We show that it may be an inappropriate method for many of the items in quality of life questionnaires, and would result in biased or misleading estimates. We provide examples of items and subscales which violate the psychometric foundations that underpin simple mean imputation. A checklist is proposed for examining the adequacy of simple imputation, and some alternative procedures are indicated.
authors.affiliation: Unit for Epidemiology and Clinical Research, Faculty of Medicine, Norwegian University of Science and Technology, Cambridge, U.K. Peter.Fayers@mrc-cto.cam.ac.uk
authors.forename: P M
authors.initials: PM
authors.lastname: Fayers
authors.forename: D
authors.initials: D
authors.lastname: Curran
authors.forename: D
authors.initials: D
authors.lastname: Machin
mesh_terms: D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D015337:Multicenter Studies as Topic; D009369:Neoplasms / Q000523:psychology* / Q000628:therapy; D010349:Patient Compliance; D011594:Psychometrics / Q000379:methods*; D011788:Quality of Life; D016032:Randomized Controlled Trials as Topic / Q000379:methods*; D011795:Surveys and Questionnaires