title: Potential biases in colorectal cancer screening using faecal occult blood test.
abstract: BACKGROUND
  Colorectal cancer (CRC) is one of the most common types of cancer in European countries and associated with a high mortality rate. A 16% relative risk reduction (RRR) of mortality was found in a meta-analysis based on four randomized controlled trials (RCT) on CRC screening. The aim of this paper was to scrutinize these trials for potential biases and assess their influence on the screening trials.
  
  
  METHODS
  The four RCTs were reviewed based on the principles of 'Critical Appraisal of the Medical Literature'. Principal investigators of the four RCTs were contacted to clarify uncertainties in their study. Data were collected from The Danish Data Archives. Authors of the Cochrane review were contacted.
  
  
  RESULTS
  Six biases were identified, of which five favour screening. Three of the biases identified were specific to CRC screening: type of diagnostic method, place of surgery and diagnostic delay.
  
  
  CONCLUSIONS
  The 16% RRR in CRC mortality found in the updated Cochrane review's meta-analysis is overestimated.
authors.affiliation: Research Unit and Section of General Practice, Institute of Public Health, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Dea Grip
authors.initials: DG
authors.lastname: Riboe
authors.forename: Tilde Steen
authors.initials: TS
authors.lastname: Dogan
authors.forename: John
authors.initials: J
authors.lastname: Brodersen
mesh_terms: D015982:Bias; D015179:Colorectal Neoplasms / Q000175:diagnosis* / Q000453:epidemiology / Q000601:surgery; D016208:Databases, Factual; D003718:Denmark / Q000453:epidemiology; D055088:Early Detection of Cancer; D006801:Humans; D013058:Mass Spectrometry; D009780:Occult Blood; D016032:Randomized Controlled Trials as Topic; D012107:Research Design