title: An empirical comparison of methods for analyzing correlated data from a discrete choice survey to elicit patient preference for colorectal cancer screening.
abstract: BACKGROUND
  A discrete choice experiment (DCE) is a preference survey which asks participants to make a choice among product portfolios comparing the key product characteristics by performing several choice tasks. Analyzing DCE data needs to account for within-participant correlation because choices from the same participant are likely to be similar. In this study, we empirically compared some commonly-used statistical methods for analyzing DCE data while accounting for within-participant correlation based on a survey of patient preference for colorectal cancer (CRC) screening tests conducted in Hamilton, Ontario, Canada in 2002.
  
  
  METHODS
  A two-stage DCE design was used to investigate the impact of six attributes on participants' preferences for CRC screening test and willingness to undertake the test. We compared six models for clustered binary outcomes (logistic and probit regressions using cluster-robust standard error (SE), random-effects and generalized estimating equation approaches) and three models for clustered nominal outcomes (multinomial logistic and probit regressions with cluster-robust SE and random-effects multinomial logistic model). We also fitted a bivariate probit model with cluster-robust SE treating the choices from two stages as two correlated binary outcomes. The rank of relative importance between attributes and the estimates of β coefficient within attributes were used to assess the model robustness.
  
  
  RESULTS
  In total 468 participants with each completing 10 choices were analyzed. Similar results were reported for the rank of relative importance and β coefficients across models for stage-one data on evaluating participants' preferences for the test. The six attributes ranked from high to low as follows: cost, specificity, process, sensitivity, preparation and pain. However, the results differed across models for stage-two data on evaluating participants' willingness to undertake the tests. Little within-patient correlation (ICC ≈ 0) was found in stage-one data, but substantial within-patient correlation existed (ICC = 0.659) in stage-two data.
  
  
  CONCLUSIONS
  When small clustering effect presented in DCE data, results remained robust across statistical models. However, results varied when larger clustering effect presented. Therefore, it is important to assess the robustness of the estimates via sensitivity analysis using different models for analyzing clustered data from DCE studies.
authors.affiliation: Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, ON, Canada.
authors.forename: Ji
authors.initials: J
authors.lastname: Cheng
authors.forename: Eleanor
authors.initials: E
authors.lastname: Pullenayegum
authors.forename: Deborah A
authors.initials: DA
authors.lastname: Marshall
authors.forename: John K
authors.initials: JK
authors.lastname: Marshall
authors.forename: Lehana
authors.initials: L
authors.lastname: Thabane
mesh_terms: D002170:Canada; D002755:Choice Behavior; D016000:Cluster Analysis; D015179:Colorectal Neoplasms / Q000175:diagnosis* / Q000523:psychology; D003661:Decision Support Techniques; D036262:Empirical Research; D005260:Female; D019538:Health Care Surveys; D006801:Humans; D016015:Logistic Models; D008297:Male; D008403:Mass Screening / Q000379:methods*; D008875:Middle Aged; D057240:Patient Preference / Q000706:statistics & numerical data*; D012107:Research Design; D012680:Sensitivity and Specificity; D011795:Surveys and Questionnaires