Age-period-cohort effects on stroke mortality in Sweden 1969-1993 and forecasts up to the year 2003

Background and Purpose Variations in stroke mortality could be explained by changes in factors that act around the time of death (period effect) and by risk factors that are present in early life (cohort effect). The aim of this study was to analyze mortality rates for stroke in Sweden during the period 1969 through 1993 and to predict mortality trends until the year 2003, taking into account age, cohort, and period effects. Methods Age-period-cohort models were used to analyze stroke mortality in Sweden between 1969 and 1993 and to predict age-specific death rates and total number of deaths for the periods 1994 through 1998 and 1999 through 2003. Results Mortality rates in the age group 25 to 89 years decreased from 203 to 143 per 100 000 for men and from 185 to 113 per 100 000 for women over the study period (average annual decrease of 1.3% for men and 1.9% for women). The decline was present in all age groups. The full age-period-cohort model provided an acceptable fit in both sexes. Predictions based on these models gave a mortality rate of 122 and 92 per 100 000 for the period 1999-2003 in men and women, respectively. Despite an aging and increasing population, the total number of stroke deaths in Sweden is predicted to decline by approximately 10% in both men and women from 1989-1993 to 1999-2003. Conclusions Both factors, cohort and calendar period, contain relevant information to explain the decline in stroke mortality trends in Sweden. Predictions indicate that the decline of both age-specific and total mortality will continue.