R Taylor1, E Comino, A Bauman. 1. Department of Public Health and Community Medicine, Faculty of Medicine, University of Sydney, NSW, Australia.
Abstract
STUDY OBJECTIVE: To investigate asthma mortality during 1920-94 in Australia in order to assess the relative role of period and birth cohort effects. DESIGN: Asthma mortality (both sexes) was age standardised and examined for changes over time. The data were also examined for age, period, and cohort (APC) effects using Poisson regression modelling. SETTING: National Australian mortality data. PARTICIPANTS: Population (both sexes) aged 15-34 years, 1920-94. MAIN RESULTS: Age adjusted period rates indicate an increase in asthma mortality during the 1950's, and increases and subsequent falls (epidemics) during the mid 1960s and late 1980s. APC modelling suggested an increasing cohort effect (adjusted for both age and period) from the birth cohort 1950-54 onwards. Period effects (adjusted for age and cohort) are characterized by an increase in the 1950s (possibly due to changes in diagnostic labelling), minimal or no increases in the mid 1960s and late 1980s (where period peaks had been noted when data were adjusted for age only), and declines in mortality risk subsequent to the periods where age-period analysis had noted increases. Thus, in Australia, some of the mid 1960s epidemic in asthma deaths, and all of the late 1980s mortality increase, seem to be attributable to cohort effects. CONCLUSIONS: The increase in asthma mortality cohort effect is consistent with empirical evidence of recent increases in prevalence (and presumably incidence) of asthma in Australia, and suggests the need for more research into the underlying environmental aetiology of this condition.
STUDY OBJECTIVE: To investigate asthma mortality during 1920-94 in Australia in order to assess the relative role of period and birth cohort effects. DESIGN: Asthma mortality (both sexes) was age standardised and examined for changes over time. The data were also examined for age, period, and cohort (APC) effects using Poisson regression modelling. SETTING: National Australian mortality data. PARTICIPANTS: Population (both sexes) aged 15-34 years, 1920-94. MAIN RESULTS: Age adjusted period rates indicate an increase in asthma mortality during the 1950's, and increases and subsequent falls (epidemics) during the mid 1960s and late 1980s. APC modelling suggested an increasing cohort effect (adjusted for both age and period) from the birth cohort 1950-54 onwards. Period effects (adjusted for age and cohort) are characterized by an increase in the 1950s (possibly due to changes in diagnostic labelling), minimal or no increases in the mid 1960s and late 1980s (where period peaks had been noted when data were adjusted for age only), and declines in mortality risk subsequent to the periods where age-period analysis had noted increases. Thus, in Australia, some of the mid 1960s epidemic in asthma deaths, and all of the late 1980s mortality increase, seem to be attributable to cohort effects. CONCLUSIONS: The increase in asthma mortality cohort effect is consistent with empirical evidence of recent increases in prevalence (and presumably incidence) of asthma in Australia, and suggests the need for more research into the underlying environmental aetiology of this condition.