Cox et al (1995): NZ Cancer Registry, incr incidence men, all types exc salivary tumours women, birth-cohort effects men (born 1912-1933 incr risk oral & pharyngeal cancer, 1922 onwards incr risk tongue cancer, 1912 & since 1932 incr risk nasopharyngeal cancer), none observed for women, causes (smoking & alcohol - synergistic, immigration), generational diff