title: Risk factors for breast cancer: a reanalysis of two case-control studies from 1926 and 1931.
abstract: BACKGROUND
  The first major case-control study, published by Janet Lane-Claypon in 1926, provided the first epidemiologic evidence that low fertility increases breast cancer risk. This study in the United Kingdom was replicated in 1931 by JM Wainwright using a US sample. Neither study used modern statistical inference to interpret their data. We have evaluated and reanalyzed data from both studies to assess the validity of the original conclusions about the etiology of breast cancer.
  
  
  METHODS
  We abstracted data from the published contingency tables for age at menarche, age at menopause, parity, age at marriage (as a proxy for age at first birth), and duration of lactation for each childbirth (as a proxy for lifetime duration of lactation). Study-specific odds ratios and associated 95% confidence intervals were calculated.
  
  
  RESULTS
  Findings from the quantitative reanalysis were consistent with contemporary epidemiologic evidence for age at menopause, parity, age at first birth, and duration of lactation.
  
  
  CONCLUSIONS
  Lane-Claypon's scientific efforts, as manifested in the 1926 UK study, are an excellent example of how one investigator's work can help develop a field of scientific inquiry.
authors.affiliation: Department of Public Health and Primary Care, University of Cambridge, Cambridge, United Kingdom. david.press@ago.org
authors.forename: David J
authors.initials: DJ
authors.lastname: Press
authors.forename: Paul
authors.initials: P
authors.lastname: Pharoah
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D001943:Breast Neoplasms / Q000209:etiology*; D016022:Case-Control Studies; D016001:Confidence Intervals; D003627:Data Interpretation, Statistical; D005260:Female; D049673:History, 20th Century; D006801:Humans; D007774:Lactation; D008393:Marriage; D008572:Menarche; D008593:Menopause; D008875:Middle Aged; D016017:Odds Ratio; D010298:Parity; D011247:Pregnancy; D015203:Reproducibility of Results; D012307:Risk Factors; D013997:Time Factors; D006113:United Kingdom; D014481:United States