Elementos de medida: Encoders y reglas ópticas

crow flies). A lower cessation prevalence was found (prevalence ratio: 0.73; 95% CI: 0.60-0.88) among men who were moderate to heavy smokers at baseline who lived <0.50 km walking distance from the nearest tobacco store compared to those living >0.50 km from a store. No effects were found for men who were light smokers at baseline or for women.

3.3 Subgroup differences

Several studies indicate that an association between density and/or proximity and smoking-related variables may be higher in specific subgroups, although few studies have investigated different subgroups within the same study. As described in the previous paragraphs, differences are found with regard to youth and adults. The following can be added:

 Several studies among the youth population indicate that the density of tobacco POS is mainly related to smoking initiation but not to established smoking (Chan & Leatherdale et al., 2011; Mc Carthy et al., 2009; Adams et al., 2013, Pokorny et al., 2003), while among adults, three out of four studies suggest that the proximity of tobacco POS is especially associated with outcomes related to smoking cessation (Kirchner et al., 2013; Halonen et al., 2013, Reitzel et al., 2011).

 There may also be an interaction with gender. One study found that susceptibility to smoking increased with an increase in the density of tobacco retailers among male, but not female, never smokers (Chan & Leatherdale, 2011).

 In addition, studies indicate that the association between density/proximity and tobacco use may be reduced by parenting practices (West et al., 2010) or local clean air policies

(Lipperman-Kreda et al., 2012).

 Socioeconomic status (SES) may modify the association between density and smoking. Chuang et al. (2005) found, for instance, that in neighbourhoods with a high density of POS, both low and high SES people had high levels of smoking, while in low density neighbourhoods, only high SES people had a lower individual smoking level.

Finally, the study by Paul et al. (2010) in Australia shows that light smokers (10 or less cigarettes per day) were more likely than heavy smokers (more than 10 cigarettes daily) to reduce or cease smoking when cigarettes were not available within walking distance of their residence or usual activities. It remains to be seen, however, whether these intentions will translate into behaviour if outlet density or proximity were to be decreased.

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3.4 Results from the literature on the density and proximity of alcohol points of sale

Compared to tobacco points of sale, the research regarding the relationship between the density and proximity of alcohol points of sale and alcohol use is more developed, especially regarding the use of prospective studies.

Stockwell et al. (2009) studied the impact of an increase in density of alcohol outlets in British Columbia on alcohol sales. The researchers concluded that there was a significant increase in per capita alcohol consumption for every 10% increase in alcohol outlet density. Similarly, Gruenewald and colleagues (1993) conducted a time series cross-sectional analysis of alcohol consumption and the density of alcohol outlets in all fifty US states. The study found that a 10% decrease in the density of outlets would reduce consumption of hard liquor by 1-3% and of wine by 4%. An additional study in New Zealand (Huckle et al., 2008) found alcohol density to be associated with quantities of alcohol consumed among teenage drinkers.

In 2009, a major review by Campbell et al. (2009) was published that led a US task force to recommend limiting the concentration of retail alcohol outlets as an important measure to curb excessive alcohol use and related harms. Importantly, the authors made a distinction between primary and secondary evidence. Primary evidence included studies comparing alcohol-related outcomes before and after a density change (that are largely missing in the tobacco literature). This category included 1) studies assessing the impact of privatising alcohol sales, commonly associated with increases in density; 2) studies assessing the impact of bans on alcohol sales, associated with decreases in density; and 3) studies on other alcohol licensing policies that directly affect outlet density. Time series analyses in which associations between changes in outlet density and alcohol-related outcomes were assessed were also included, although the cause of the

observed change in density was not known. Secondary evidence included cross-sectional studies, which do not allow inference of causality.

In this review, the following conclusions were formulated:

 All five studies that assessed the association between outlet density and population-level alcohol consumption (using a time series design) found that they were positively associated, i.e., increased density was associated with increased consumption and vice versa.

 Most of the studies included in the review found that greater outlet density was associated with increased alcohol consumption and related harms.

 Four studies of national or local licensing policy changes consistently indicated that more permissive licensing increased the number of on- and off-licence alcohol outlets, which in turn led to increased alcohol consumption, most notably among heavy drinkers in two studies.

 In addition, studies of changes over time in outlet density that were not particularly linked to policies also consistently found higher density related to higher consumption.

 The number of studies investigating the effects of reduced outlet density or a ban on sales was very limited. Insofar as studies were available, the outcomes were highly dependent on whether communities were isolated. In isolated communities (e.g., in Alaska), alcohol-

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