BACKGROUND While smoking prevalence in high income countries has declined over time, socioeconomic inequalities in smoking have widened. This study is one of the few studies to examine the longitudinal pattern of income-related smoking inequalities and only the second using concentration indices in its analysis.

METHOD Income-related smoking inequalities were measured using concentration indices using the Northern Ireland Continuous Household Survey data. Smoking inequalities were compared quantitatively and visually across three periods: 1985-1995, 1997-2005 and 2007-2015. Joinpoint analysis was used to measure the overall time trend of smoking inequalities. Subgroup analysis was used to examine the nature of change in smoking inequalities across population sub-groups.

FINDINGS Throughout 1985-2015, smoking was more concentrated among the poor (standard concentration index of-0·131, p < 0·001). While prevalence declined sharply across population, income-related inequalities increased sharply in general and within subgroups. Income-related smoking inequalities were significantly larger among high educated group and those who were employed. No structural break was observed with respect to the adoption of any specific policy measures over the period.

CONCLUSION Current approaches to tobacco control may be ill-suited to addressing smoking inequalities and may indeed be counterproductive. More tailored approaches that address the specific needs of population sub-groups or more draconian approaches such as extensions to prohibition may be required to reduce prevalence further while avoiding a widening of inequalities.