title: Using qualitative research to facilitate the interpretation of quantitative results from a discrete choice experiment: insights from a survey in elderly ophthalmologic patients.
abstract: BACKGROUND
  Age-related macular degeneration (AMD) is the leading cause of visual impairment and blindness in industrialized countries. Currently, mainly three treatment options are available, which are all intravitreal injections, but differ with regard to the frequency of injections needed, their approval status, and cost. This study aims to estimate patients' preferences for characteristics of treatment options for neovascular AMD.
  
  
  METHODS
  An interviewer-assisted discrete choice experiment was conducted among patients suffering from AMD treated with intravitreal injections. A Bayesian efficient design was used for the development of 12 choice tasks. In each task patients indicated their preference for one out of two treatment scenarios described by the attributes: side effects, approval status, effect on visual function, injection and monitoring frequency. While answering the choice tasks, patients were asked to think aloud and explain the reasons for choosing or rejecting specific characteristics. Quantitative data were analyzed with a mixed multinomial logit model.
  
  
  RESULTS
  Eighty-six patients completed the questionnaire. Patients significantly preferred treatments that improve visual function, are approved, are administered in a pro re nata regimen (as needed), and are accompanied by bimonthly monitoring. Patients significantly disliked less frequent monitoring visits (every 4 months) and explained this was due to fear of deterioration being left unnoticed, and in turn experiencing disease deterioration. Significant preference heterogeneity was found for all levels except for bimonthly monitoring visits and severe, rare eye-related side effects. Patients gave clear explanations of their individual preferences during the interviews.
  
  
  CONCLUSIONS
  Significant preference trends were discernible for the overall sample, despite the preference heterogeneity for most treatment characteristics. Patients like to be monitored and treated regularly, but not too frequently or infrequently. The results of our qualitative research facilitated the interpretation of the quantitative data collected in this study.
authors.affiliation: Institute for Health Economics and Clinical Epidemiology, Cologne University Hospital, Cologne, Germany.
authors.forename: Vera
authors.initials: V
authors.lastname: Vennedey
authors.affiliation: Institute for Health Economics and Clinical Epidemiology, Cologne University Hospital, Cologne, Germany.
authors.forename: Marion
authors.initials: M
authors.lastname: Danner
authors.affiliation: Department of Health Services Research, School for Primary Care and Public Health (CAPHRI), Maastricht University, Maastricht, the Netherlands; Department of Public Mental Health, Trimbos Institute, Netherlands Institute of Mental Health and Addiction, Utrecht, the Netherlands.
authors.forename: Silvia Maa
authors.initials: SM
authors.lastname: Evers
authors.affiliation: Department of Vitreo-Retinal Surgery, Center of Ophthalmology, Cologne University Hospital, Cologne, Germany.
authors.forename: Sascha
authors.initials: S
authors.lastname: Fauser
authors.affiliation: Institute for Health Economics and Clinical Epidemiology, Cologne University Hospital, Cologne, Germany.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Stock
authors.affiliation: Department of Clinical Epidemiology and Medical Technology Assessment, CAPHRI, University Hospital Maastricht, Maastricht, the Netherlands.
authors.forename: Carmen D
authors.initials: CD
authors.lastname: Dirksen
authors.affiliation: Department of Health Services Research, School for Primary Care and Public Health (CAPHRI), Maastricht University, Maastricht, the Netherlands.
authors.forename: Mickaël
authors.initials: M
authors.lastname: Hiligsmann
keywords: age related macular degeneration; discrete choice experiment; intravitreal injection; patient preferences; qualitative research