The results from our study indicate that many smokers see and consume single cigarettes in Mexico, in spite of the illegality of their sale. Approximately 30% of smokers saw singles for sale on a daily basis, 18% bought singles at their last purchase, and 31% bought singles in the previous month. These estimates are generally higher than estimates from 2006 , although they are not as high as found in a convenience sample of young, disadvantaged adults in the US, where 77% had purchased singles in the previous month . Our results are mostly consistent with the notion that single cigarette use in Mexico is most prevalent among younger smokers and those with lower income and educational achievement. However, associations between singles consumption and these characteristics were somewhat inconsistent across bivariate and multivariate models. More consistent positive associations were found between singles consumption and lighter intensity of cigarette consumption, greater intention to quit, and more frequent urges to smoke upon seeing the sale of singles. This suggests that singles availability may facilitate the early stages of smoking uptake among young people, but they may also maintain low levels of smoking or be used as a method to quit, as has been reported previously [3, 14].
Smokers who reported more frequent urges to smoke upon viewing single cigarettes for sale were more likely to purchase singles. However, these same people were no less likely to quit at followup than those who did not report these urges. This lack of association contrasts with cross-sectional research, which found that smokers who reported more frequent urges to smoke because of seeing singles for sale were less likely to intend to quit (AOR = 0.40) . Although our longitudinal results suggest that cueing due to the availability and visibility of singles may not maintain smoking among Mexicans, our self-report measure may not have adequately captured the cueing phenomenon, which can operate at unconscious levels. Cues to smoke have been studied very little in natural settings or through surveys , and future research should assess the reliability and validity of self-report and other measures, in order to better understand how cueing works in naturalistic settings. For example, environmental scans indicating widely varying prevalence of singles availability in Mexico , could be linked to other data on smoking among people who inhabit these environments.
Our longitudinal results regarding the use of singles as a method to quit were inconsistent. Smokers who frequently purchased singles to control their consumption were no more likely to attempt to quit than those who did not. Estimates of factors that predicted being quit for a month or more produced more inconsistent results, with no increased likelihood of being quit among smokers with the highest frequency of purchasing singles to control consumption; however, less frequent singles consumption was associated with a greater likelihood of being quit at followup (AORno urge vs. less frequent urges = 2.77, 95% CI 1.77, 4.53). When examining either quit attempts or quit success, interactions between intention to quit and the use of singles to reduce consumption were not statistically significant. Hence, it appears that when smokers impose the additional economic costs and search costs of consuming singles as a method to quit, the population-level effect as a harm reduction strategy is unclear. Furthermore, non-statistically significant results around the interactions between consumption intensity and singles consumption suggested that stratification of the data by consumption intensity does not clarify these relationships.
The current study's population-based, longitudinal nature lends strength to these conclusions. However, there were some limitations, including the need for longer studies to better understand relapse, which could be greater in environments with higher prevalence of cues to smoke due to the availability of singles. Furthermore, attrition may have biased results, particularly as the followup sample was slightly more likely to notice singles than those who were not followed up (31% vs. 27% noticing daily). Nevertheless, this difference was not substantial and there were no differences between the analytic sample and those lost to followup on the primary indicators of singles consumption and perceptions. Participation in the study may have been biased in ways that preclude generalization to the sampling frame, although the direction of this bias is not possible to ascertain because of the lack of data on nonparticipants.
The results from this study may not generalize to Mexican populations outside of the sampling frame. However, data were collected in the largest cities in Mexico, and 70% of the Mexican population lives in urban areas . Furthermore, the prevalence of smoking is three times higher in urban areas than in rural areas . Hence, the results likely generalize to the segment of the population that bears a substantial part of the tobacco-related disease burden in Mexico. Similar studies should be conducted with smokers in other settings, including in populations outside of Mexico that have heavier smoking patterns, as the light smoking pattern among Mexicans may restrict these conclusions to Mexico. Finally, a fuller treatment of the implications of singles availability for tobacco control policy development would attempt to address whether smokers who switch from packs to singles would have otherwise quit in the face of interventions, such as tax increases. This type of assessment would likely demand quasiexperimental designs which could compare smoking behavior in countries with different levels of singles availability.