Trends in socio-economic differentials in cigarette smoking behaviour between 1990 and 1998: a large prospective study in Korean men.

OBJECTIVES: To investigate the magnitude and time trends in socio-economic differentials in cigarette smoking behaviour. STUDY DESIGNS: A prospective observational study of male civil servants followed-up for 8 years. SETTING: All civil service offices in Korea. PARTICIPANTS: A total of 322,991 male civil servants aged 30-49 years on whom information on monthly salary was available and who had reported cigarette smoking behaviour between 1990 and 1998. RESULTS: Smoking prevalence was 60.1% in 1990 and was inversely associated with salary level. The difference in smoking prevalence between the highest and the lowest salary groups gradually widened from 13.0% in 1990 to 16.1% in 1998. The relative index of inequality (RII) as a measure of socio-economic inequality in smoking behaviour was 1.91 [95% confidence interval (CI) 1.86-1.97] in 1990 and increased between 1990 and 1998. The RII for smoking cessation was 0.60 in 1990 (95% CI 0.58-0.62) and gradually decreased as time lapsed. CONCLUSIONS: An increasing trend in socio-economic inequality in smoking behaviour was observed in this study.