Smoking remains one of the leading preventable causes of premature death worldwide [
1]. Smokers who smoke approximately 16 cigarettes per day lose about 11 min of their lifetime per cigarette smoked [
2]. Additionally, smoking is an important risk factor for serious health problems and life-threatening diseases such as lung cancer, coronary heart disease and stroke [
1]. Despite the knowledge about the negative consequences of smoking, in 2016 every fourth person aged 15 and older smoked in Switzerland [
3]. High relapse rates indicate that quitting smoking is a major challenge [
4]. The core of relapse prevention is to strengthen the capability to manage high-risk situations (e.g., cue-induced cravings [
5,
6]). Although many evidence-based smoking cessation interventions exist (e.g., behavioral counselling, medications, nicotine replacement therapy [
7]), the majority of smokers quit unassisted without the help of pharmacological aids or other interventions [
8,
9]. The accessibility and availability of mobile technology (e.g., mobile phones/smartphones) offers new promising opportunities for cost-effective interventions in everyday life [
10]. As most relapses occur within the first weeks after the quit attempt [
4,
11], such interventions have the potential to deliver support when it is most needed [
11,
12].
In 2016 mobile-broadband networks reached 84% of the global population [
13]. Among a sample of US and UK smokers the prevalence of smartphone ownership with internet access with over 75% was high [
14]. In the context of smoking cessation, there are already numerous studies on text messages based interventions using mobile phones [
15]. The efficacy of these interventions is tentatively confirmed as positive effects were found up to 6 months after quitting smoking [
16,
17]. In contrast, there are far fewer smartphone app-based smoking cessation intervention studies in daily life [
18]. Due to the high prevalence of smartphone usage, delivering health promotion interventions using smartphone apps is a promising approach, especially because of the proximity to users, cost effectiveness, location independence, possibility of tailoring and providing instant interactive support [
19‐
21].
First studies on smartphone apps and smoking cessation provide good evidence that apps are a useful tool to promote the implementation of the intended behavior (c.f., [
10,
22]). For example, preliminary results of the SmokeFree28 app showed higher cessation rates for 28 days than unaided cessation [
23]. Also, in a RCT of the smartphone app REQ-Mobile smokers who used the app showed higher abstinence rates at 30 days compared to smokers who did not use the app [
10]. Furthermore, in another RCT smokers who received a smartphone app to quit were more likely to be continuously abstinent at 1 month, 3 months and 6 months after quitting [
22]. All those apps assessed smoking abstinence by self-report only.
In a content analysis of smartphone apps for smoking cessation, calculator apps were the most common category (38.8% of all apps), followed by hypnosis apps (17.3%), rationing apps (15.3%), trackers (12.2%), informational apps (6.1%), games (3.1%) and lung health testers (2.0%) [
20]. In line with these findings, another content analysis of Android smoking cessation apps also found that apps predominantly provide simple tools, as for example calculators, calendars, trackers or distractors [
24]. Most available apps used very little evidence-based content to support quit attempts [
19]. In approximately 55% (
n = 75) of the apps no behavior change techniques (BCTs [
25];) were present [
19]. Apps rarely referenced smokers outside of the app to a quit helpline or provided opportunities to reach out for social support from a social network member [
20]. Of 225 rated Android apps only 6 (2.7%) had also content regarding social support for smokers [
24]. However, one of the key recommendation of the clinical practice guideline Treating Tobacco Use and Dependence [
7] is to deliver social support in individual, group or telephone counseling settings. External resources such as social support seem promising in helping smokers to quit and might buffer the daily stress smokers experience while quitting [
4,
11,
26].
Social support and smoking cessation
Social support comprises resources provided to a person in need and can include the following functions: emotional (e.g., comforting, encouraging) and instrumental (practical help or assistance) [
27,
28]. It can be distinguished into a recipient’s retrospective report of support received (i.e.,
received support), a provider’s retrospective report of support given (i.e.,
provided support), and the perceived prospective potential access to social support resources (i.e.,
perceived support) [
27‐
29]. There is evidence from longitudinal, prospective studies that higher received social support from a network member is related to higher abstinence rates (e.g., [
30]). In a recent intensive longitudinal mobile phone-based study with single-smoker couples the fine-grained temporal dynamics of daily social support and daily number of cigarettes smoked was investigated in the process of quitting [
26]. Increases in received emotional and instrumental support were related to less smoking, and effects were more pronounced after a self-set quit date when support is most needed. Also, support provided from the non-smoking romantic partner was associated with less smoking [
26]. Consistent with these findings, in another intensive longitudinal mobile phone-based study with dual-smoker couples, received emotional and instrumental support was related to less smoking after a joint self-set quit date [
31]. For men only, female partner’s provided emotional and instrumental support was also related to fewer cigarettes smoked in dual-smoker couples [
31].
Up to date, several intervention studies exist to foster social support [
32]. However, results on the effectiveness are mixed [
33,
34]. In a review investigating RCTs that compared smokers who received an intervention to enhance peer or partner support with smokers who did not receive the support intervention, the effectiveness of the social support interventions was not clearly given [
35]. In another review there was also lack of evidence regarding the efficacy of the use of buddies in community interventions [
11]. For example, in a study examining the effectiveness of a social support intervention with a buddy in a group treatment program to aid smoking cessation, smokers in the buddy condition (smokers were paired with another participant to provide mutual support) were no more likely than smokers in the control condition to stay abstinent at one, four or 26 weeks [
36]. Thus, it seems that buddy systems so far have been unable to improve abstinence rates of participants in group treatment programs.
Findings from intervention studies could, thus, not demonstrate the assumed effectiveness of partner or peer support on smoking cessation, supposably because these interventions were not successful in increasing social support in the first place [
11,
37,
38]. One of the problems associated with this could be that these buddy systems often rely on unacquainted buddies, not persons from one’s own personal social network. Moreover, buddies need instructions on how to support smokers during a quit attempt to ensure high quality of social support. The ideal timing of support seems relevant; that is, when in the process of smoking cessation social support is most helpful for smokers [
11,
39]. This emphasizes that future intervention studies enhancing social support should take place in smoker’s everyday life and social support should be available directly when smokers need it. This issue can be addressed by applying ecological momentary interventions (EMI [
40];) that are characterized by the delivery to people as they go about their everyday lives in combination with momentary ambulatory assessments [
40]. EMI’s can be used to stimulate processes that take place in everyday life, as for example social support. Thus, a smartphone app for targeting social support in the context of smoking cessation would allow not only to address the aspect of timing but could also provide the target person with tailored social support while quitting. There is first evidence from a randomized pilot trial comparing automated text-messaging support (control group) with automated text-messaging support plus personalized texts from a peer mentor who formerly smoked (peer-mentor group) that smoking abstinence at 3 months was higher for the group with peer mentors compared to the control group [
41]. However, the role of social support from a network member via a smartphone app has not yet been investigated in the context of smoking cessation. The present study investigates the efficacy of such a smartphone app, the SmokeFree Buddy app, connecting a smoker with a freely chosen support buddy to promote smoking cessation in smoker’s everyday life using a randomized controlled trial (RCT).
The SmokeFree buddy app
As part of the tobacco prevention campaign in Switzerland the Federal Office of Public Health (FOPH) and its partners developed a smartphone app –the SmokeFree Buddy app - to encourage smokers’ intention to quit and to offer social support interactively from a self-chosen person (buddy) while quitting smoking. The SmokeFree Buddy app was developed from experts based on the empirical and theoretical evidence of social support from a social network member for smoking cessation. Mobile interventions have the potential to intervene at any time, in a tailored manner and during actual experiences in people’s everyday life [
40]. The SmokeFree Buddy app, thus, aims at enabling smokers to quit with the help of a self-chosen buddy from one’s social network and offers the possibility of enhancing social support resources and availability directly after a self-set quit attempt in smoker’s everyday life. The buddy then gets instructed via the smartphone app on how to support the smoker during his/her quit attempt. In addition to self-reported smoking behavior the present RCT uses an objective device to assess smoking abstinence via a “smokerlyzer” with a corresponding smartphone app and is therefore, the first study assessing smoking abstinence objectively on a daily basis.
A general criticism on standard RCT’s is that the level of longitudinal assessment is usually on a macro-time level (e.g., baseline and a 1 month follow-up). This is also the case for intervention studies on social support in the context of smoking cessation (i.e., [
11,
37,
38]). However, relatively little is known on when an intervention reaches its effect and what time window would be appropriate to capture it. As such, the choice for the follow-up time points is often made on an arbitrary basis. By using micro-time assessments (e.g., daily) during an ongoing intervention, it is possible to answer questions on how an intervention effect unfolds over time, when it reaches its maximal effect and whether it is maintained or levels off quickly [
42]. Moreover, it allows investigating how people respond differently to the intervention. In the present study, we combine micro-time and macro-time assessments by using an intensive longitudinal intervention design with three end-of-day diary periods across 6 months. The 6 months time period was chosen for better comparability with previous studies using a six-month follow-up.