BIRTH COHORT ANALYSIS OF THE PREVALENCE OF CHRONIC COUGH IN IRAN- BASED ON NATIONAL HEALTH SURVEYS IN 1991 AND 1999

This cross- sectional study was done to assess the prevalence of chronic cough by age and date of birth (age-period-cohort analysis). Using data from two National Health Surveys in 1991 and 1999 (involving cross-sectional general population samples), we studied all cases of chronic cough recorded during the period of 1991 to 1999 in people aged 2 to 70 years. A birth cohort analysis was performed on the data. Comparison with earlier surveys showed that the prevalence of chronic cough had fallen from 4.5% to 1.8%. Age-period-cohort analyses of the age effect revealed that prevalence rate of chronic cough increased with age but in every age group it actually decreased after the 8-year period. The fact that different trends are observed in cross-sectional and cohort data points to a strong cohort effect. the prevalence of chronic cough is strongly determined by a person’s year of birth. Also for any given age group, prevalence rates were lower in younger compared to older cohorts.