title: Do prevalence expectations affect patterns of visual search and decision-making in interpreting CT colonography endoluminal videos?
abstract: OBJECTIVE
  To assess the effect of expected abnormality prevalence on visual search and decision-making in CT colonography (CTC).
  
  
  METHODS
  13 radiologists interpreted endoluminal CTC fly-throughs of the same group of 10 patient cases, 3 times each. Abnormality prevalence was fixed (50%), but readers were told, before viewing each group, that prevalence was either 20%, 50% or 80% in the population from which cases were drawn. Infrared visual search recording was used. Readers indicated seeing a polyp by clicking a mouse. Multilevel modelling quantified the effect of expected prevalence on outcomes.
  
  
  RESULTS
  Differences between expected prevalence were not statistically significant for time to first pursuit of the polyp (median 0.5 s, each prevalence), pursuit rate when no polyp was on screen (median 2.7 s(-1), each prevalence) or number of mouse clicks [mean 0.75/video (20% prevalence), 0.93 (50%), 0.97 (80%)]. There was weak evidence of increased tendency to look outside the central screen area at 80% prevalence and reduction in positive polyp identifications at 20% prevalence.
  
  
  CONCLUSIONS
  This study did not find a large effect of prevalence information on most visual search metrics or polyp identification in CTC. Further research is required to quantify effects at lower prevalence and in relation to secondary outcome measures.
  
  
  CONCLUSIONS
  Prevalence effects in evaluating CTC have not previously been assessed. In this study, providing expected prevalence information did not have a large effect on diagnostic decisions or patterns of visual search.
authors.affiliation: 1 Nuffield Department of Primary Care Health Sciences, University of Oxford, Oxford, UK.
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Fanshawe
authors.affiliation: 2 Health and Medical Sciences Group, University of Cumbria, Lancaster, UK.
authors.forename: Peter
authors.initials: P
authors.lastname: Phillips
authors.affiliation: 3 Centre for Medical Imaging, University College London, London, UK.
authors.forename: Andrew
authors.initials: A
authors.lastname: Plumb
authors.affiliation: 3 Centre for Medical Imaging, University College London, London, UK.
authors.forename: Emma
authors.initials: E
authors.lastname: Helbren
authors.affiliation: 3 Centre for Medical Imaging, University College London, London, UK.
authors.forename: Steve
authors.initials: S
authors.lastname: Halligan
authors.affiliation: 3 Centre for Medical Imaging, University College London, London, UK.
authors.forename: Stuart A
authors.initials: SA
authors.lastname: Taylor
authors.affiliation: 4 Applied Vision Research Centre, Loughborough University, Loughborough, UK.
authors.forename: Alastair
authors.initials: A
authors.lastname: Gale
authors.affiliation: 5 Public Health, Epidemiology and Biostatistics, Institute of Applied Health Sciences, University of Birmingham, Birmingham, UK.
authors.forename: Susan
authors.initials: S
authors.lastname: Mallett
mesh_terms: D000328:Adult; D059031:Anticipation, Psychological; D002983:Clinical Competence / Q000592:standards*; D000066491:Clinical Decision-Making / Q000379:methods*; D003111:Colonic Polyps / Q000000981:diagnostic imaging; D023881:Colonography, Computed Tomographic / Q000592:standards*; D005133:Eye Movements / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D011871:Radiology / Q000592:standards*; D014741:Video Recording; D014796:Visual Perception