Period effects, generation effects and age effects in peptic ulcer mortality.

The interpretation of secular trends in terms of period, age and cohorts is illustrated by data on peptic ulcer mortality for England and Wales from 1900 to 1977. Approaches to the external validation of the inferences made from such analyses are also illustrated. These data conform with predictions from a cohort analysis of some 20 years ago that peptic ulcer mortality and morbidity would decline.