The association between tobacco outlet density and smoking among young people: A systematic methodological review

AIM: Evidence on the association between tobacco outlet density and proximity and smoking behavior among youth is inconsistent, which may be due to methodological problems in some studies. We assessed the association of outlet density or proximity with smoking behavior among young people while taking into account the methodological quality of studies. METHODS: MEDLINE, EMBASE, and Google Scholar were systematically searched for studies on the relationship between outlet density or proximity and smoking behavior among 12- to 25-year-olds, published between 1997 and 2017. Methodological quality of the included studies was evaluated independently by two reviewers. RESULTS: Twenty studies were included in the review. The quality assessment identified five primary sources of potential bias: overadjustment for mediators (problems identified in 14 studies), underadjustment for confounders (six studies), poor statistical model fit (four studies), selection bias (three studies), and misclassification of exposure measurements (eight studies). Four studies were of high methodological quality. In studies with relatively high quality, 10 associations were reported, of which seven were nonsignificant, two positive, and one negative. Similarly, the complete body of evidence demonstrated mostly nonsignificant associations, but a larger proportion of positive associations than negative. CONCLUSION: Although there is some support for a positive direction, current literature does not provide consistent evidence for a positive association between outlet density and smoking among youth. This is not necessarily due to bias in specific studies, but more to fundamental challenges in study design and exposure measurements. These issues need to be addressed in future studies using more rigorous methods. IMPLICATIONS: Our findings suggest that, although there is some evidence for a positive association, current scientific literature does not provide consistent support to claim an effect of tobacco outlet density or proximity on youth smoking. This underlines the need for more research with improved methodology. There is a need for quasiexperimental studies, in which the outlet density changes substantially, studies measuring the actual exposure of youth to tobacco outlets, and qualitative research on the mechanisms underlying any association.