An assessment of the impact of informative dropout and nonresponse in measuring health-related quality of life using the EuroQol (EQ-5D) descriptive system

Objectives: 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.