title: Patients' & healthcare professionals' values regarding true- & false-positive diagnosis when colorectal cancer screening by CT colonography: discrete choice experiment.
abstract: OBJECTIVE
  To establish the relative weighting given by patients and healthcare professionals to gains in diagnostic sensitivity versus loss of specificity when using CT colonography (CTC) for colorectal cancer screening.
  
  
  METHODS
  Following ethical approval and informed consent, 75 patients and 50 healthcare professionals undertook a discrete choice experiment in which they chose between "standard" CTC and "enhanced" CTC that raised diagnostic sensitivity 10% for either cancer or polyps in exchange for varying levels of specificity. We established the relative increase in false-positive diagnoses participants traded for an increase in true-positive diagnoses.
  
  
  RESULTS
  Data from 122 participants were analysed. There were 30 (25%) non-traders for the cancer scenario and 20 (16%) for the polyp scenario. For cancer, the 10% gain in sensitivity was traded up to a median 45% (IQR 25 to >85) drop in specificity, equating to 2250 (IQR 1250 to >4250) additional false-positives per additional true-positive cancer, at 0.2% prevalence. For polyps, the figure was 15% (IQR 7.5 to 55), equating to 6 (IQR 3 to 22) additional false-positives per additional true-positive polyp, at 25% prevalence. Tipping points were significantly higher for patients than professionals for both cancer (85 vs 25, p<0.001) and polyps (55 vs 15, p<0.001). Patients were willing to pay significantly more for increased sensitivity for cancer (p = 0.021).
  
  
  CONCLUSIONS
  When screening for colorectal cancer, patients and professionals believe gains in true-positive diagnoses are worth much more than the negative consequences of a corresponding rise in false-positives. Evaluation of screening tests should account for this.
authors.affiliation: Centre for Medical Imaging, University College London, London, United Kingdom.
authors.forename: Darren
authors.initials: D
authors.lastname: Boone
authors.affiliation: Department of Primary Care Health Sciences, University of Oxford, Oxford, United Kingdom.
authors.forename: Susan
authors.initials: S
authors.lastname: Mallett
authors.affiliation: Department of Public Health and Epidemiology, Birmingham University, Birmingham, United Kingdom.
authors.forename: Shihua
authors.initials: S
authors.lastname: Zhu
authors.affiliation: Faculty of Medicine, University of Southampton, Southampton, United Kingdom.
authors.forename: Guiqing Lily
authors.initials: GL
authors.lastname: Yao
authors.affiliation: Centre for Medical Imaging, University College London, London, United Kingdom.
authors.forename: Nichola
authors.initials: N
authors.lastname: Bell
authors.affiliation: Department of Epidemiology and Public Health, University College London, London, United Kingdom.
authors.forename: Alex
authors.initials: A
authors.lastname: Ghanouni
authors.affiliation: Department of Epidemiology and Public Health, University College London, London, United Kingdom.
authors.forename: Christian
authors.initials: C
authors.lastname: von Wagner
authors.affiliation: Centre for Medical Imaging, University College London, London, United Kingdom.
authors.forename: Stuart A
authors.initials: SA
authors.lastname: Taylor
authors.affiliation: Centre for Statistics in Medicine, University of Oxford, Oxford, United Kingdom.
authors.forename: Douglas G
authors.initials: DG
authors.lastname: Altman
authors.affiliation: Department of Public Health and Epidemiology, Birmingham University, Birmingham, United Kingdom.
authors.forename: Richard
authors.initials: R
authors.lastname: Lilford
authors.affiliation: Centre for Medical Imaging, University College London, London, United Kingdom.
authors.forename: Steve
authors.initials: S
authors.lastname: Halligan
mesh_terms: D003111:Colonic Polyps / Q000175:diagnosis; D023881:Colonography, Computed Tomographic / Q000523:psychology*; D015179:Colorectal Neoplasms / Q000175:diagnosis*; D055088:Early Detection of Cancer / Q000523:psychology; D006801:Humans; D010361:Patients / Q000523:psychology; D012680:Sensitivity and Specificity