title: [Is the benefit of organized mass screening for cervix cancer and breast cancer in Norway scientifically justified?].
abstract: BACKGROUND
  It has been argued that mass screening may reduce mortality from cervical cancer and breast cancer in Norway by 50% and 39%, respectively. However, some authors doubt that mass screening for breast cancer is justifiable. This article discusses whether mass screening for cervical cancer in Norway is more effective than opportunistic screening.
  
  
  METHODS
  The scientific methods used to justify organised mass screening for cervical cancer are reviewed and discussed, as are the randomised trials used to justify screening by mammography. The author is especially critical of the use of descriptive statistics to justify screening, on the assumption that there is a basic constant incidence or mortality rate.
  
  
  RESULTS
  The incidence rates of pre-malignant conditions and cervical cancer in Norway are presented. There is no essential increase in the number of pre-malignant conditions after three years of organised mass screening compared to the previous three-year of unorganized screening. However, the number of pre-malignant conditions did increase from 1987 to 1992 due to a national recommendation for testing every three years. By contrast, incidence rates for cervical cancer remained almost constant in the 1987-97 period.
  
  
  CONCLUSIONS
  There is no scientific proof of organised mass screening for cervical cancer being preferable to unorganized screening. The author warns against only comparing observed rates with historic rates and rates in other countries; alternatively, rates among those who participate in the screening might be compared in a simultaneous analysis to rates among those who do not respond to the invitation. The author also suggests estimating correlation coefficients between individual test results to identify high-risk individuals.
authors.affiliation: Seksjon for medisinsk statistikk Universitetet i Oslo.
authors.forename: P H
authors.initials: PH
authors.lastname: Zahl
mesh_terms: D001943:Breast Neoplasms / Q000000981:diagnostic imaging* / Q000401:mortality / Q000517:prevention & control; D005069:Evaluation Studies as Topic; D005260:Female; D006801:Humans; D008327:Mammography; D008403:Mass Screening / Q000379:methods; D009664:Norway; D002583:Uterine Cervical Neoplasms / Q000000981:diagnostic imaging* / Q000401:mortality / Q000517:prevention & control; D014626:Vaginal Smears