title: An assessment of the impact of informative dropout and nonresponse in measuring health-related quality of life using the EuroQol (EQ-5D) descriptive system.
abstract: OBJECTIVE
  To investigate the impact of imputing EQ-5D values to allow for informative dropout and nonresponse in a longitudinal assessment of the health-related quality of life (HRQL) of liver transplant recipients.
  
  
  METHODS
  The EQ-5D was administered at defined time intervals pre- and post-transplantation to all adults who were listed to receive liver transplants as National Health Service (NHS) treatment at each of the six Department of Health designated centers in England and Wales over a time-period of 36 months (12 month recruitment period and 24 month follow-up period). During the course of the study missing data arose for two main reasons, informative dropout and nonresponse. Informative dropout was accounted for by giving those patients who died an EQ-5D score of 0 and those patients who were too ill to respond to an EQ-5D score equivalent to the 5th percentile of respondents for each time point pretransplantation. Nonresponse was accounted for using relatively naive approaches (last value carried forward, and upper/lower 95% confidence interval around the mean) and contrasted with a more sophisticated multiple imputation method.
  
  
  RESULTS
  Adjusting for informative dropout in isolation resulted in a marked deterioration in mean scores over time pretransplant relative to the base case situation in which no such adjustments were made. Nevertheless, adjusting for informative dropout and/or nonresponders did not alter the base case conclusion of no statistically significant differences in mean EQ-5D scores over time pretransplant. In contrast, post-transplant data indicated highly statistically significant improvements in quality of life over time for the base case (P < 0.001) whereas no statistically significant improvements over time were found when informative dropout was allowed for in isolation (P = 0.402) or when informative dropout and nonresponse were allowed for simultaneously (P = 0.105-0.185).
  
  
  CONCLUSIONS
  It is important that future studies which purport to assess the HRQL over time of patients, such as these with end-stage liver disease, include an allowance for informative dropout and nonresponse within the analysis.
authors.affiliation: Sheffield Health Economics Group, School of Health and Related Research, University of Sheffield, Regent Court 30, Regent Street, Sheffield S1 4DA, UK. j.ratcliffe@sheffield.ac.uk
authors.forename: Julie
authors.initials: J
authors.lastname: Ratcliffe
authors.forename: Tracey
authors.initials: T
authors.lastname: Young
authors.forename: Louise
authors.initials: L
authors.lastname: Longworth
authors.forename: Martin
authors.initials: M
authors.lastname: Buxton
mesh_terms: D015982:Bias; D002755:Choice Behavior; D003627:Data Interpretation, Statistical; D004739:England / Q000453:epidemiology; D005500:Follow-Up Studies; D006304:Health Status; D006801:Humans; D007258:Informed Consent / Q000523:psychology / Q000706:statistics & numerical data; D016031:Liver Transplantation / Q000193:education / Q000401:mortality / Q000523:psychology; D009010:Monte Carlo Method; D015999:Multivariate Analysis; D016011:Normal Distribution; D010352:Patient Dropouts / Q000193:education / Q000523:psychology / Q000706:statistics & numerical data; D010353:Patient Education as Topic; D019057:Quality-Adjusted Life Years; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires / Q000592:standards*; D016019:Survival Analysis; D013727:Terminal Care; D013997:Time Factors; D014852:Wales / Q000453:epidemiology