Socioeconomic differentials in the immediate mortality effects of the national Irish smoking ban

Abstract

Background: Consistent evidence has demonstrated that smoking ban policies save lives, but impacts on health inequalities are uncertain as few studies have assessed post-ban effects by socioeconomic status (SES) and findings have been inconsistent. The aim of this study was to assess the effects of the national Irish smoking ban on ischemic heart disease (IHD), stroke, and chronic obstructive pulmonary disease (COPD) mortality by discrete and composite SES indicators to determine impacts on inequalities.

Methods: Census data were used to assign frequencies of structural and material SES indicators to 34 local authorities across Ireland with a 2000-2010 study period. Discrete indicators were jointly analysed through principal component analysis to generate a composite index, with sensitivity analyses conducted by varying the included indicators. Poisson regression with interrupted time-series analysis was conducted to examine monthly age and gender-standardised mortality rates in the Irish population, ages ≥35 years, stratified by tertiles of SES indicators. All models were adjusted for time trend, season, influenza, and smoking prevalence.

Results: Post-ban mortality reductions by structural SES indicators were concentrated in the most deprived tertile for all causes of death, while reductions by material SES indicators were more equitable across SES tertiles. The composite indices mirrored the results of the discrete indicators, demonstrating that post-ban mortality decreases were either greater or similar in the most deprived when compared to the least deprived for all causes of death.

Conclusions: Overall findings indicated that the national Irish smoking ban reduced inequalities in smoking-related mortality. Due to the higher rates of smoking-related mortality in the most deprived group, even equitable reductions across SES tertiles resulted in decreases in inequalities. The choice of SES indicator was influential in the measurement of effects, underscoring that a differentiated analytical approach aided in understanding the complexities in which structural and material factors influence mortality.

Figure 1. Immediate Post-Smoking Ban Effects^§ on Cause-Specific Mortality by Structural Measures of Socioeconomic Status, Ages ≥35 Years, Republic of Ireland, 2000–2010*.

^§Age and gender-standardised and adjusted for time trend, season, influenza, and smoking prevalence. *‘Least’ refers to the least deprived tertile, ‘Inter’ to the intermediate tertile, and ‘Most’ to the most deprived tertile IHD  =  ischemic heart disease COPD  =  chronic obstructive pulmonary disease. ^†Significantly different from least deprived tertile at 95% confidence level. ^‡Significantly different from least deprived tertile at 90% confidence level.

Figure 2. Immediate Post-Smoking Ban Effects^§ on Cause-Specific Mortality by Material Measures of Socioeconomic Status, Ages ≥35 Years, Republic of Ireland, 2000–2010*.

^§Age and gender-standardised and adjusted for time trend, season, influenza, and smoking prevalence. *‘Least’ refers to the least deprived tertile, ‘Inter’ to the intermediate tertile, and ‘Most’ to the most deprived tertile IHD  =  ischemic heart disease COPD  =  chronic obstructive pulmonary disease. ^†Significantly different from least deprived tertile at 95% confidence level. ^‡Significantly different from least deprived tertile at 90% confidence level.

Figure 3. Immediate Post-Smoking Ban Effects^§ on Cause-Specific Mortality by Composite Measures^¶ of Socioeconomic Status, Ages ≥35 Years, Republic of Ireland, 2000–2010*.

^§Age and gender-standardised and adjusted for time trend, season, influenza, and smoking prevalence. ^¶Baseline Index includes Low Education, Manual Occupation, Non-Irish/Non-UK Nationality, ≥5 Person Families, Male Unemployment, Rented/Free Housing Tenure, and No Car Access. Sensitivity Index 1 includes Baseline Index and High Education. Sensitivity Index 2 substitutes Male Unemployment with Population Unemployment. Sensitivity Index 3 substitutes Male Unemployment with Population Unemployment and excludes Nationality. *‘Least’ refers to the least deprived tertile, ‘Inter’ to the intermediate tertile, and ‘Most’ to the most deprived tertile. IHD  =  ischemic heart disease COPD  =  chronic obstructive pulmonary disease. ^†Significantly different from least deprived tertile at 95% confidence level. ^‡Significantly different from least deprived tertile at 90% confidence level.