Effect of Age, Birth Cohort, and Period of Death on Cerebrovascular Mortality in Spain, 1952 Through 1991

Abstract

Background and Purpose The continued decrease in cerebrovascular disease in Spain remains unexplained. Age-period-cohort analysis enables description of birth cohort and period-of-death components. This study sought to describe these effects on the decline of stroke mortality in Spain. Methods Deaths due to cerebrovascular diseases in the period from 1952 through 1991 and the corresponding population figures were grouped into 11 age groups and 8 5-year periods, from which age-specific mortality rates for 18 birth cohorts were then computed. These were plotted for graphical presentation purposes and fitted to Poisson regression models to assess age, period, and cohort effects. Results An exponential age effect was present for both sexes regardless of cohort or period. A definite downward period effect was observable from 1962 to 1991, except for a sharp fall and peak in the periods 1967 to 1971 and 1972 to 1976, respectively, which was possibly ascribable to changes in diagnostic and coding practices. Age- and period-adjusted stroke mortality increased for earlier cohorts and decreased for generations born between 1892 and 1940. For post-1940 generations, there was an increasing risk of stroke mortality. Conclusions The results suggest that a decrease in incidence coupled with an increase in survival may account for the observed decline in stroke mortality, but further studies on the Spanish population are needed to assess these findings. Although not yet definitive, there are signs of an increase in incidence among the more recent generations. If the decreasing period effect fails to offset this increase, future years may see a deceleration in the current decline in stroke mortality.