title: Assessing quality of life in a randomized clinical trial: correcting for missing data.
abstract: BACKGROUND
  Health-related quality of life is a topic of current interest. This paper considers a randomized phase III study of radiation therapy with concurrent chemotherapy (docetaxel) versus radiation therapy alone in non-small cell lung cancer, stage III A/B. Longitudinal data on quality of life have been obtained through repeated administration of a multi-item questionnaire (EORTC QLQ-C30) developed by the European Organisation for Research and Treatment of Cancer. Missingness in the data is owing to patients having failed to complete the questionnaire at some of the scheduled filling-in times.
  
  
  METHODS
  We have analysed a monotone (in terms of missingness) subset of the data as regards estimation of the mean score of a summary measure of self-reported quality of life in a hypothetical drop-out-free population at different points in time. Missingness is a difficult issue of great importance. We have therefore chosen to compare three different methods that are relatively easy to implement: the linear-increments method, the inverse-probability-weighting method and the Markov-process method. Single imputation has been applied in a supplementary analysis to fill in for all the non-consecutive missing score values prior to the execution of the estimation procedure.
  
  
  RESULTS
  For the response in focus, the observed mean score at a certain time is larger than the estimated mean scores, which implies that the true mean score is easily overestimated unless the missingness is appropriately adjusted for. Comparison of the treatment arms shows a significant difference in mean score at the end of treatment.
  
  
  CONCLUSIONS
  Use of proper methodology developed for analysing data subject to missingness is necessary to reduce potential estimation bias. The quality of life of patients receiving radiation therapy with concurrent chemotherapy (docetaxel) appears somewhat worse than that of patients receiving radiation therapy alone in the period during which treatment is given. The conclusions are robust for the choice of statistical methods.
authors.affiliation: Department of Biostatistics, University of Oslo, P,O, Box 1122 Blindern, N-0317 Oslo, Norway. nina.gunnes@medisin.uio.no
authors.forename: Nina
authors.initials: N
authors.lastname: Gunnes
authors.forename: Taral G
authors.initials: TG
authors.lastname: Seierstad
authors.forename: Steinar
authors.initials: S
authors.lastname: Aamdal
authors.forename: Paal F
authors.initials: PF
authors.lastname: Brunsvig
authors.forename: Anne-Birgitte
authors.initials: AB
authors.lastname: Jacobsen
authors.forename: Stein
authors.initials: S
authors.lastname: Sundstrøm
authors.forename: Odd O
authors.initials: OO
authors.lastname: Aalen
mesh_terms: D000970:Antineoplastic Agents / Q000627:therapeutic use; D002289:Carcinoma, Non-Small-Cell Lung / Q000188:drug therapy / Q000532:radiotherapy*; D017024:Chemotherapy, Adjuvant; D000077143:Docetaxel; D005260:Female; D006801:Humans; D016014:Linear Models; D008137:Longitudinal Studies; D008297:Male; D008390:Markov Chains; D011336:Probability; D011788:Quality of Life; D013223:Statistics as Topic / Q000379:methods*; D011795:Surveys and Questionnaires; D043823:Taxoids / Q000627:therapeutic use
chemical_list: D000970:Antineoplastic Agents; D043823:Taxoids; D000077143:Docetaxel