title: Undescended testis and the risk of testicular cancer: importance of source and classification of exposure information.
abstract: BACKGROUND
  The strength of the association between undescended testis and testicular cancer varies considerably across studies. Here we report the effect of various classifications of self-reported history of undescended testis and different data sources on the estimates of the risk of testicular cancer from a case-control study.
  
  
  METHODS
  We performed a population-based case-control study including 269 testicular cancer cases and 797 controls matched on age and region. Medical history was assessed by interviews (index persons) and mailed questionnaires (mothers). We used conditional logistic regression to calculate odds ratios (OR) and kappa coefficients to assess agreement between different sources of information.
  
  
  RESULTS
  Odds ratios for testicular cancer ranged between 2.4 and 5.4 based on the sons' self-reports and between 1.1 and 1.9 based on the mothers' reports. The agreement between the sons and mothers on undescended, gliding or retractile testis was fair (kappa 0.53) and was good when these conditions were treated by surgery (kappa 0.89). The rating of a history of undescended testis by two urologists was fair (kappa 0.54).
  
  
  CONCLUSIONS
  The questionnaire design, the classifications of undescended testis and data sources have an important impact on the OR for the association of undescended testis and testicular cancer. These factors may partially explain the heterogeneity of the OR for this association in case-control studies relying on self-reports.
authors.affiliation: Institute for Medical Informatics, Biometry and Epidemiology, University Hospital of Essen, Hufelandstr. 55, 45122 Essen, Germany. andreas.stang@uni-essen.de
authors.forename: A
authors.initials: A
authors.lastname: Stang
authors.forename: W
authors.initials: W
authors.lastname: Ahrens
authors.forename: K
authors.initials: K
authors.lastname: Bromen
authors.forename: C
authors.initials: C
authors.lastname: Baumgardt-Elms
authors.forename: I
authors.initials: I
authors.lastname: Jahn
authors.forename: C
authors.initials: C
authors.lastname: Stegmaier
authors.forename: S
authors.initials: S
authors.lastname: Krege
authors.forename: K H
authors.initials: KH
authors.lastname: Jöckel
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D003456:Cryptorchidism / Q000453:epidemiology*; D015340:Epidemiologic Research Design; D005858:Germany / Q000453:epidemiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D012307:Risk Factors; D011795:Surveys and Questionnaires; D013736:Testicular Neoplasms / Q000453:epidemiology*