title: Crowdsourcing as a novel technique for retinal fundus photography classification: analysis of images in the EPIC Norfolk cohort on behalf of the UK Biobank Eye and Vision Consortium.
abstract: OBJECTIVE
  Crowdsourcing is the process of outsourcing numerous tasks to many untrained individuals. Our aim was to assess the performance and repeatability of crowdsourcing for the classification of retinal fundus photography.
  
  
  METHODS
  One hundred retinal fundus photograph images with pre-determined disease criteria were selected by experts from a large cohort study. After reading brief instructions and an example classification, we requested that knowledge workers (KWs) from a crowdsourcing platform classified each image as normal or abnormal with grades of severity. Each image was classified 20 times by different KWs. Four study designs were examined to assess the effect of varying incentive and KW experience in classification accuracy. All study designs were conducted twice to examine repeatability. Performance was assessed by comparing the sensitivity, specificity and area under the receiver operating characteristic curve (AUC).
  
  
  RESULTS
  Without restriction on eligible participants, two thousand classifications of 100 images were received in under 24 hours at minimal cost. In trial 1 all study designs had an AUC (95%CI) of 0.701(0.680-0.721) or greater for classification of normal/abnormal. In trial 1, the highest AUC (95%CI) for normal/abnormal classification was 0.757 (0.738-0.776) for KWs with moderate experience. Comparable results were observed in trial 2. In trial 1, between 64-86% of any abnormal image was correctly classified by over half of all KWs. In trial 2, this ranged between 74-97%. Sensitivity was ≥ 96% for normal versus severely abnormal detections across all trials. Sensitivity for normal versus mildly abnormal varied between 61-79% across trials.
  
  
  CONCLUSIONS
  With minimal training, crowdsourcing represents an accurate, rapid and cost-effective method of retinal image analysis which demonstrates good repeatability. Larger studies with more comprehensive participant training are needed to explore the utility of this compelling technique in large scale medical image analysis.
authors.affiliation: National Institute for Health Research Biomedical Research Centre at Moorfields Eye Hospital & University College London Institute of Ophthalmology, London, United Kingdom.
authors.forename: Danny
authors.initials: D
authors.lastname: Mitry
authors.forename: Tunde
authors.initials: T
authors.lastname: Peto
authors.forename: Shabina
authors.initials: S
authors.lastname: Hayat
authors.forename: James E
authors.initials: JE
authors.lastname: Morgan
authors.forename: Kay-Tee
authors.initials: KT
authors.lastname: Khaw
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Foster
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019540:Area Under Curve; D018070:Biological Specimen Banks; D003362:Cost-Benefit Analysis; D063045:Crowdsourcing; D003930:Diabetic Retinopathy / Q000175:diagnosis; D003941:Diagnostic Techniques, Ophthalmological; D005654:Fundus Oculi; D006801:Humans; D008875:Middle Aged; D015588:Observer Variation; D010781:Photography / Q000379:methods*; D012372:ROC Curve; D015203:Reproducibility of Results; D012164:Retinal Diseases / Q000175:diagnosis*; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires; D006113:United Kingdom