title: Quality Control Process for EQ-5D-5L Valuation Studies.
abstract: BACKGROUND
  The values of the five-level EuroQol five-dimensional questionnaire (EQ-5D-5L) are elicited using composite time trade-off and discrete choice experiments. Unfortunately, data quality issues and interviewer effects were observed in the first few EQ-5D-5L valuation studies. To prevent these issues from occurring in later studies, the EuroQol Group established a cyclic quality control (QC) process.
  
  
  OBJECTIVE
  To describe this QC process and show its impact on data quality.
  
  
  METHODS
  A newly developed QC tool provided information about protocol compliance, interviewer effects, and mean values by health state severity. In a cyclic process, this information is initially used to evaluate whether new interviewers meet minimal quality requirements and later to provide feedback about how their performance may be improved. To investigate the impact of this cyclic process, we compared the quality of the data in Dutch and Spanish valuation studies that did not have this QC process with that in the follow-up studies in the same countries that used the QC process. Data quality was measured using protocol violations, variability between interviewers, the proportion of inconsistent responders, and clustering of composite time trade-off values.
  
  
  RESULTS
  In Spain, protocol violations were reduced from 87% in the valuation study to 5% in the follow-up study and in the Netherlands from 20% to 8%. In both countries, interviewers performed more homogeneously in the follow-up studies. The number of inconsistent respondents was reduced by 23.2% in Spain and 23.6% in the Netherlands. Values were less clustered in the follow-up studies.
  
  
  CONCLUSIONS
  The implementation of a strict QC process in EQ-5D-5L valuation studies increases interviewer protocol compliance and promotes data quality.
authors.affiliation: Executive Office, EuroQol Research Foundation, Rotterdam, The Netherlands. Electronic address: jramos@euroqol.org.
authors.forename: Juan M
authors.initials: JM
authors.lastname: Ramos-Goñi
authors.affiliation: Executive Office, EuroQol Research Foundation, Rotterdam, The Netherlands.
authors.forename: Mark
authors.initials: M
authors.lastname: Oppe
authors.affiliation: Executive Office, EuroQol Research Foundation, Rotterdam, The Netherlands.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Slaap
authors.affiliation: Section of Medical Psychology, Department of Psychiatry, Erasmus MC, Rotterdam, The Netherlands.
authors.forename: Jan J V
authors.initials: JJ
authors.lastname: Busschbach
authors.affiliation: Executive Office, EuroQol Research Foundation, Rotterdam, The Netherlands; Institute for Health Policy and Management, Erasmus University, Rotterdam, The Netherlands.
authors.forename: Elly
authors.initials: E
authors.lastname: Stolk
mesh_terms: D006304:Health Status; D006305:Health Status Indicators; D006801:Humans; D007407:Interviews as Topic; D009426:Netherlands; D011786:Quality Control; D011788:Quality of Life; D015203:Reproducibility of Results; D018434:Sickness Impact Profile; D013030:Spain; D011795:Surveys and Questionnaires
keywords: economic; health status index; life valuation; quality control; quality of life