Summary: | female breast cancer show marked international variation, being higher in western countries, and having risen in recent years in a number of countries (Saracci & Repetto, 1978). These time changes have been analysed to a variable degree of detail for a limited number of populations (Bjarnson et al., 1974; Armstrong, 1976; Moolgavkar et al., 1979). These analyses indicate that the increases may be satisfactorily accounted for by: (a) a "pure" generation (birth cohort) effect; this applies to the incidence data of Iceland, Osaka (Japan) and Denmark, for the last the effect being modified by age; (b) some
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