BACKGROUND
There are many smoking cessation interventions proven to help smokers quit30–32. Clinical practice guidelines suggest a range from individual, group, and telephone counseling to the use of seven first-line medications (5 nicotine and 2 non-nicotine)5. Furthermore, quitline counseling is shown to be effective among diverse populations33,34. The Kick it for Good intervention utilized many of these evidence-based practices to encourage smokers to quit. While analyses have shown that the intervention increased overall quit rates in the TTA-MI group compared to TTA-SC, it is of clinical significance to determine how public housing smokers quit and contributing factors to successful abstinence.
Examining mediators and moderators of successful cessation may help identify which components of the TTA intervention increases smoking cessation and provides insight on which sub-populations may benefit the most. These findings can thus support dissemination and implementation efforts. This is especially salient since these questions have yet to be explored in a socioeconomically disadvantaged population.
Hypothesized potential mediators of the KIG intervention include utilization of the Massachusetts Quitline or local clinic-based programs, NRT use,
motivation to quit, and self-efficacy to quit. The use of quit lines, local
clinic-based programs, and NRT are intended mediators of the intervention as TTAs encouraged participants to use these evidence-based methods to quit5.
Increasing motivation to quit and self-efficacy to quit were also targets of the TTA intervention as they have been shown to predict smoking cessation35–37.
Furthermore, the Transtheoretical Model, a health behavior change theory, proposes that motivation to quit and self-efficacy to quit should predict intention to quit, quit attempts, and smoking cessation38. Thus, motivation to quit and self-efficacy to quit were assessed as potential mediators of the intervention effect on smoking abstinence.
It is unknown whether the hypothesized mediators are part of the indirect effect of the KIG intervention. Other studies of cessation interventions that have examined potential mediators using mediational analyses have shown that increases in self-efficacy, changes in smoking temptations, and partner support contribute to cessation39–41. However, these mediation analyses and others have relied on product methods, originally outlined by Baron and Kenny20. This
approach was the standard in epidemiology until the advent of a method rooted in the counterfactual framework published in 2013 by Valeri and Vanderweele21. The utility of the counterfactual method over the product method is its ability to break down the total effect of the exposure on outcome into direct and indirect effects even in models where interactions and nonlinearities occur. When it is of interest to assess whether the effect is mediated by a specific pathway or other hypothesized mediators, the decomposition of the total effect into separate direct
and indirect effects is useful. The current study utilizes this approach to examine mediation in the context of the KIG intervention.
Finally, there are factors, some especially relevant to socioeconomically disadvantaged populations that may moderate the KIG intervention effect, including gender, age, ethnicity, nicotine dependence, presence of other smokers, perceived stress, and social support. Younger age34 and Black or Hispanic race/ethnicity42,43 are associated with reduced likelihood of cessation.
Women are less likely to respond to nicotine replacement therapy and have lower quit rates compared to men44,45. Poor psychosocial functioning, including depressed mood and high levels of perceived stress, are also associated with poor cessation outcomes46–48. Certain smoking characteristics, such as high nicotine dependence and the presence of other smokers in the household, may reduce the likelihood of successful cessation49–51. Social support is known to be associated with increased probability of quitting smoking, particularly among low-income and ethnically diverse populations14,15,34,52. These variables were chosen for their known associations with smoking cessation, although they have yet to be investigated as potential moderators in the context of a smoking cessation intervention for public housing residents. Additionally, moderation analyses have generally been assessed using methods of interaction term significance,
stratification, or comparison of group-specific estimates34. We compared the potential differing effects of the KIG intervention among sub-groups by using methods based on biological interactions53.
The aim of this study was to assess the mechanisms through which the KIG intervention effects occur (mediators) and identify the groups for whom the intervention has the greatest effect (moderators) on smoking cessation. We hypothesize the intervention will directly affect hypothesized mediators: Quitline or local clinic program use, NRT use, motivation to quit, and self-efficacy to quit.
The mediators will in turn affect 30-day point prevalence abstinence at 3-month and 12-month follow-up. Gender, age, ethnicity, nicotine dependence level, presence of other smokers, stress, and social support will moderate the effect of the intervention on 30-day point prevalence abstinence at follow-up. Specifically, the greatest effects of the intervention will be observed among those who are young, White, male, have lower nicotine dependence, do not live with other smokers, report lower stress, and have higher social support.
METHODS