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proximity was found to be related to smoking cessation (Halonen et al., 2013) and smoking

abstinence after a quit attempt (Reitzel et al., 2011). However, the latter relationship between the proximity of POS and quitting could not be replicated in a second study (Han et al., 2014).

Individual study results

A study among 12.529 adults aged 15 years and older in New Zealand investigated whether neighbourhood access to a retail outlet selling tobacco was associated with individual smoking behaviour (Pearce et al., 2009). To establish the accessibility to outlets selling tobacco, the travel time by car from the population-weighted centroid of the neighbourhood to the nearest

supermarket or convenience store was calculated. After controlling for individual-level demographic and socioeconomic variables, individuals living in the quartiles of neighbourhoods with the best access to supermarkets (OR 1.23; 95% CI= 1.06-1.42) and convenience stores (OR 1.19, 95% CI= 1.03-1.38) had higher odds of smoking compared with individuals in the worst access

quartiles. However, the relationship between neighbourhood accessibility to these retail outlets and smoking disappeared once neighbourhood–level variables (deprivation and rurality) were included in the analyses. Based on their findings, the authors conclude that, once adjusted for

neighbourhood deprivation, there is little evidence for an association between better locational access to tobacco retail stores and individual-level smoking behaviour in New Zealand. Kirchner et al (2013) examined whether individuals in Washington DC who experienced an

increased craving to smoke as their daily point-of-sale tobacco exposure increased would be more likely to relapse. The study was carried out among 475 smokers aged >18 years who had quit smoking for at least 24 hours. Exposure to point-of-sale tobacco retailers was measured by geolocation tracking via the participants' mobile phones. The phones recorded the location of the person every fifteen minutes over the first month of a quit attempt. This information was combined with the POS locations. On average, the participants had 2.7 contacts with a POS per day. Lapsing was more likely to occur on days with any POS contact (OR=1.19; 95% CI: 1.18-1.20), and it increased when the number of contacts with POS increased (OR=1.07; 95% CI: 1.06-1.08). Furthermore, the analyses showed that the incremental effect of another POS contact was highly significant (mean OR=1.26) and fairly stable (range 1.11-1.38). Contrary to expectation, the association between POS contacts and lapsing was especially strong in the absence of craving (OR=1.22; 95% CI: 1.20-1.23), whereas it progressively decreased by 9% when it was associated with low craving levels (OR=1.13; 95% CI: 1.12-1.14) and decreased by another 13% and to non- significance when associated with high daily craving (OR=1.0; 95% CI: 0.99-1.01). The authors concluded that, overall, daily exposure to POS was associated with lapsing when craving was low. A study among 8121 women and men aged 25-74 in four Californian cities (Chuang et al. 2005) assessed the effects of neighbourhood-level socioeconomic status and convenience store proximity on individual smoking after consideration of individual-level characteristics. Convenience stores were used to measure tobacco availability, as they account for the largest proportion of tobacco sales. The straight line distance from the participant's home to the nearest convenience store was measured. Data were used from five cross-sectional surveys between 1979 and 1990. The results

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showed a high correlation between living near a convenience store and neighbourhood SES, with a higher percentage of respondents in low SES neighbourhoods living close to a convenience store (49%) compared to respondents in high SES neighbourhoods (18%). Regression analyses showed that people living close to a convenience store smoked more than people living farther away (b=- 0.182). The results remained the same after accounting for individual characteristics (b=-.154). Reitzel et al. (2011) followed a cohort of 414 racially/ethnically diverse adult daily smokers from Houston, Texas enrolled in a quit attempt. Their study examined the effect of outlet proximity9

(measured at distances of 250 m and 500 m) on continuous smoking abstinence 6 months after a quit attempt. All analyses controlled for demographics and tobacco-related variables, and smoking abstinence was biochemically verified. The proximity of the participant's home to the closest tobacco outlet was a significant predictor of smoking abstinence 6 months later. This applied to both the 250 m proximity measure (OR=0.54; 95% CI=0.33-0.87) and the 500 m measure (OR=0.68; 95% CI=0.46-0.99). For an explanation of their findings, the authors refer to a large body of evidence that supports that smoking cues can provoke subjective and autonomic responses among smokers, including an increase in craving, which might increase the risk of relapse. They suggest that a single outlet in close proximity to the home might be enough to complicate quit attempts by offering easy access to cigarettes when an urge to smoke strikes. The authors suggest that zoning laws restricting POS around residential areas may be an important addition to existing regulations.

The study by Reitzel et al. (2011) was replicated in England by Han et al. (2014). Data were used from a cohort of 611 smokers participating in an RCT assessing the impact of nicotine replacement therapy. Participants were recruited from 29 general practices in two English cities. In this study, the effects of outlet proximity on continuous abstinence after six months were measured. At the six-month follow-up, 66 participants had quit. Contrary to Reitzel et al. (2011), the results showed that smoking abstinence at six months was not predicted by the proximity of residences to the closest tobacco outlet. The authors give several possible explanations for the differing results. First, the participants in the Han et al. study were recruited via general practices in which all smokers were written to, and those motivated to both stop smoking and participate in the RCT were recruited. By contrast, Reitzel et al. (2011) contacted smokers through print and radio

advertisements. This might have resulted in a group with lower motivation to quit smoking, which might have made them more sensitive to tobacco retail outlets. An additional possible explanation for the different findings suggested by the authors is the lack of a licensing system or a retail register in the UK, which might have resulted in inaccuracies in mapping the retail outlets.

Another cohort study with quitting as the outcome variable was conducted in Finland by Halonen et al. (2013). This study used data from a cohort of adults (76% women) working in the public sector and examined whether the proximity to outlets stores within 0.5 km of the person’s home was associated with smoking cessation among adult men and women. Baseline data were used from the period 1997-2005, and follow-up data were from 2008 and 2009. Forty percent of the participants quit smoking during the follow-up (a mean of 5.5 years). Proximity was measured both as the

9 _{Outlet proximity was measured along the road network. This is preferable to the 'as the crow flies' method, as}

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