title: Implications of birth cohort patterns in interpreting trends in breast cancer rates.
abstract: BACKGROUND
  Most investigations of trends in cancer rates are based on a cross-sectional approach, i.e., an examination of trends in rates by year of diagnosis or death. When there are longitudinal effects (i.e., trends in rates with successive birth cohorts), interpretation of cross-sectional trends can be misleading. Based on cross-sectional comparisons, U.S. breast cancer mortality rates have been reported to be decreasing over the last 20 years in younger women but to be increasing during the same period in older women.
  
  
  OBJECTIVE
  To examine the impact of longitudinal effects on the divergence of cross-sectional trends in breast cancer mortality with age, we examined breast cancer mortality rates from 1969 to 1988 by birth cohort for White women in the United States.
  
  
  METHODS
  By using a novel, nonparametric, permutational method to analyze 2-year, age-specific mortality rates for women aged 30-89 years, we identified trends in rates with successive birth cohorts.
  
  
  RESULTS
  The divergence in trends with age is shown to be consistent with an increase in breast cancer risk with successive birth cohorts from 1900 to 1916 and with a decrease in breast cancer risk with successive birth cohorts beginning around 1926.
  
  
  CONCLUSIONS
  Longitudinal effects have a significant impact on cross-sectional trends in breast cancer mortality.
  
  
  CONCLUSIONS
  Continuation of the birth cohort trend in younger women, which could correspond to changes in reproductive patterns accompanying the "baby boom," would result in decreasing cross-sectional trends in women 60-69 years of age over the next decade and in women 70-79 years of age in the subsequent decade. Longitudinal effects must be taken into consideration when monitoring and evaluating the effects of early detection, treatment, and intervention programs using national rates.
authors.affiliation: Division of Cancer Prevention and Control, National Cancer Institute, Bethesda, MD 20892.
authors.forename: R E
authors.initials: RE
authors.lastname: Tarone
authors.forename: K C
authors.initials: KC
authors.lastname: Chu
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000453:epidemiology* / Q000401:mortality; D015331:Cohort Studies; D004812:Epidemiologic Methods; D005260:Female; D006801:Humans; D015994:Incidence; D008875:Middle Aged; D008954:Models, Biological; D015233:Models, Statistical; D012306:Risk; D015996:Survival Rate; D014481:United States