How a 5-Day Stay in the Tobacco-Free Environment of the Stoptober House Supports Individuals to Quit Smoking: A Mixed Methods Pilot Study

Abstract Introduction: The Stoptober House is part of the annual national Stoptober smoking cessation campaign in the Netherlands. During the first week of October, 48 volunteers resided in the tobacco-free Stoptober House for 5 days and received smoking cessation counseling. This pilot study explored how the Stoptober House may have facilitated smoking cessation among participants. Methods: We included 48 individuals who were selected for the Stoptober House (intervention group) and 67 individuals who were not selected (control group). Surveys were conducted at baseline, immediately after 2 and 8 weeks of post-intervention. We compared self-reported abstinence, psychosocial mediators related to smoking cessation, and perceived active elements of the Stoptober House between the intervention and control groups using t/χ2 tests and linear mixed model (LMM) analysis. Sixteen semi-structured qualitative interviews were conducted to explore participants’ perspectives on the elements contributing to their success in quitting smoking. Results: At 8 weeks of follow-up, a higher proportion of participants in the intervention group (24/48 [50%]) reported being abstinent compared to the control group (5/67 [7%]; p < 0.001). Among participants who reported making a quit attempt, 22/38 (57.9%) in the intervention group remained abstinent compared to 4/17 (23.5%) in the control group (p = 0.022). The intervention group also exhibited higher self-efficacy to quit smoking throughout the follow-up period and higher social support immediately after the Stoptober House. No significant differences were observed in other psychosocial factors. The interviews highlighted several perceived elements of the Stoptober House that contributed to smoking cessation success, including restricted smoking opportunities, access to smoking cessation counselors, and peer support. Conclusion: This pilot study suggests that the Stoptober House provides support that can help people quit smoking. Further research is needed to confirm these findings and determine the cost-effectiveness of this intervention in promoting long-term abstinence among specific groups of smokers.

Introduction: The Stoptober House is part of the annual national Stoptober smoking cessation campaign in the Netherlands.During the first week of October, 48 volunteers resided in the tobacco-free Stoptober House for 5 days and received smoking cessation counseling.This pilot study explored how the Stoptober House may have facilitated smoking cessation among participants.Methods: We included 48 individuals who were selected for the Stoptober House (intervention group) and 67 individuals who were not selected (control group).Surveys were conducted at baseline, immediately after 2 and 8 weeks of postintervention.We compared self-reported abstinence, psychosocial mediators related to smoking cessation, and perceived active elements of the Stoptober House between the intervention and control groups using t/χ 2 tests and linear mixed model (LMM) analysis.Sixteen semi-structured qualitative interviews were conducted to explore participants' perspectives on the elements contributing to their success in quitting smoking.Results: At 8 weeks of follow-up, a higher proportion of participants in the intervention group (24/48 [50%]) reported being abstinent compared to the control group (5/67 [7%]; p < 0.001).Among participants who reported making a quit attempt, 22/38 (57.9%) in the intervention group remained abstinent compared to 4/17 (23.5%) in the control group (p = 0.022).The intervention group also exhibited higher self-efficacy to quit smoking throughout the follow-up period and higher social support immediately after the Stoptober House.No significant differences were observed in other psychosocial factors.The interviews highlighted several perceived elements of the Stoptober House that contributed to smoking cessation success, including restricted smoking opportunities, access to smoking cessation counselors, and peer support.Conclusion: This pilot study suggests that the Stoptober House provides support that can help people quit smoking.Further research is needed to confirm these findings and determine the cost-effectiveness of this intervention in promoting long-term abstinence among specific groups of smokers.

Introduction
Tobacco smoking is a major health threat and remains the leading preventable cause of death [1,2].There are several treatments for smoking cessation, including pharmacotherapy and individual or group behavioral counseling [3,4].The effectiveness of behavioral counseling is greater when it is more intensive, for example, when the duration and number of sessions are increased [5][6][7].However, even with the combination of behavioral counseling and pharmacotherapy, only a minority of people who smoke remain abstinent for more than 12 months [6].People who have difficulty quitting smoking may benefit from more intensive smoking cessation support, such as residential smoking cessation treatment [8][9][10][11][12][13].Residential treatment or inpatient treatment takes place in an environment that is free of smoking cues and provides the opportunity for counseling that is higher in frequency and duration [9].Residential treatment could help individuals through the first days of a quit attempt when the risk of relapse is high [9,14].In many countries, residential treatment for smoking cessation is not yet available as a treatment option.
The "Stoptober House," an intervention developed in the Netherlands, can be considered a form of short residential treatment.The Stoptober House is part of the annual "Stoptober" mass media campaign, which originated in England in 2012 and was adopted in the Netherlands in 2014, encouraging people to quit smoking for 28 days in October [15,16].During the first week of October, fifty volunteers are "locked up" in the Stoptober House in the Netherlands.The idea of the Stoptober House is that participants make a public commitment to quit smoking and then begin their quit attempt in a tobacco-free environment where they receive social support from peers and guidance from professional counselors.During the 5-day stay, participants are offered a full-day program with presentations on smoking addiction and smoking cessation, small group sessions led by a smoking cessation counselor, and various social, creative, and sports activities to keep participants engaged and distracted from smoking.The activities in the Stoptober House are filmed and can be viewed via a livestream on the Stoptober campaign website.
The aim of this pilot study was to explore whether participation in the Stoptober House increases quit success.In addition, this study aimed to gain insight into which elements of the Stoptober House helped participants stay abstinent.

Study Design
The study was conducted from September to December 2019, employing a quasi-experimental mixed methods design.The research involved a quantitative analysis of data gathered via online surveys and a qualitative component, utilizing in-depth interviews.Participants gave their written informed consent to participate in the study.This study was not subject to the Dutch Medical Research Involving Human Subjects Act (WMO), and therefore ethical approval was not required [17].The effectiveness of the Stoptober House was assessed by comparing the percentage of quitters between individuals who were selected to spend 5 days in the Stoptober House and individuals who registered but were not selected for the Stoptober House.Participants in the study completed four online surveys: a baseline survey 2 weeks before the start of the Stoptober House (T0), a survey immediately (<1 week, T1), 2 weeks (T2), and 8 weeks (T3) after the end of the Stoptober House.In addition, semi-structured qualitative interviews were conducted with 16 participants on the fourth and fifth days of their stay in the Stoptober House.

Intervention
Participants in the intervention group stayed at the Stoptober House for 5 days, from September 30 to October 4, 2019.The participants agreed to attend the smoking cessation counseling sessions and stay in the house, but if they wanted to leave the house, they could go home.The program consisted of counseling sessions in groups of 12 or 13 people led by a professional smoking cessation coach, presentations about smoking and addiction, and various workshops and activities.Participants in the control group could continue to participate in Stoptober through the Stoptober mobile app [18], which provides information and support for quitting smoking.

Participants
The Stoptober organization recruited participants for the Stoptober House through social media channels and the Stoptober website.The house had a capacity for 50 people.Of the 250 people who applied for the Stoptober House, 50 were manually selected by the Stoptober organization using a matrix to ensure a sufficient number of participants from different provinces, both men and women, of different ages, with different levels of education, and with variation in daily cigarette consumption.The control group consisted of those who also applied for the Stoptober house but were not selected due to limited space in the house.The same matrix was used to obtain an approximately comparable control group.Of the 50 people invited to the Stoptober House, 1 person was excluded from participation due to pneumonia, and a second person was unable to participate due to work commitments.The 48 participants who were selected for the Stoptober House and the individuals who were not selected for the house were invited by e-mail to participate in the surveys.Eligible participants were people who smoked tobacco and were at least 18 years old.

Baseline Measurements
At baseline, respondents were asked about their age, sex, education level, previous quit attempts, nicotine dependence (Heaviness of Smoking Index [19]), and motivation to quit smoking (Motivation to Stop Scale [20]).Determination ("I am determined to remain abstinent during Stoptober") and confidence ("I am confident that I will be able to remain abstinent during Stoptober") [21] were measured on a Likert scale from 1 (totally disagree) to 5 (totally agree).Smoking Abstinence At T1, participants were asked whether they had made a quit attempt (yes or no).Point prevalence abstinence was measured at each measurement by asking, "Do you currently smoke (sometimes) or do you not smoke at all?".Participants who responded that they did not smoke at all were categorized as abstinent.

Psychosocial Mediators
We assessed attitude, self-efficacy, and social norms for quitting smoking at each measurement (T0 to T3).Attitude toward quitting was measured by the statement, "If I quit/ continue to quit smoking within the next 2 months, that would be. .."This statement could be rated on a five-point Likert scale from 1 (totally disagree) to 5 (totally agree) and was presented with three endings: (1) "sensible," (2) "enjoyable," and (3) "positive" [22].Cronbach's α was 0.68.Self-efficacy to quit smoking was measured by six questions asking whether respondents would be able to refrain from smoking when offered a cigarette, when being stressed, after a meal, when going to a bar, when drinking alcohol, and when drinking coffee or tea [23].The six items could be answered on a scale from 1 (totally disagree) to 5 (totally agree).Cronbach's α was 0.76.Social norm was measured with three statements: "Most people I know don't smoke; most people I know think it's normal not to smoke; people I know want me to stop smoking."Response categories ranged from 1 (totally disagree) to 5 (totally agree).Cronbach's α was 0.62.On T1 to T3, we asked participants how much support they received from: family members, acquaintances, and friends (1 = very little support to 5 = a lot of support; Cronbach's α = 0.90).We also assessed how much pressure to quit they felt from family members, acquaintances, and friends (1 = very little pressure to 5 = a lot of pressure; Cronbach's α = 0.91).All scales were constructed by averaging the items into a single score.

Stoptober House Elements
At baseline, we assessed which elements of the Stoptober House were reasons for participants to register.Participants could choose from the following options (multiple answers allowed): different environment from home, quitting together with others, no objects around that remind me of smoking, no cigarettes available, media attention/cameras, coaching sessions.Directly after the end of the Stoptober House (T1), we asked the intervention group to what extent these elements had contributed to their quitting success (1 = helped very little to 5 = helped a lot).All participants were asked how much Stoptober had helped them to quit smoking, and the intervention group was asked how much the Stoptober House had helped them to quit smoking (1 = helped very little to 5 = helped a lot).The presence of smoking cues in the environment was measured for all participants at T1 with the question, "In the period since the last questionnaire (end of September), how often have you seen something (for example, a pack of cigarettes, a lighter, or an ashtray) that made you crave for a cigarette?"(1 = very often to 5 = never).Difficulty to smoke was measured for all participants at T1 with the question, "How difficult or easy has it been for you to get cigarettes since the last questionnaire (end of September)?" (1 = very easy to 5 = very difficult).

Statistical Analyses
Quantitative data were analyzed using IBM SPSS Statistics for Windows (version 26.0, Armonk, NY, USA: IBM Corp.).For the analysis of smoking abstinence, we used an intention-to-treat approach; respondents lost to follow-up were considered smokers.Because of the small number of abstinent participants in the control group, it was not possible to control for baseline differences in the analyses of smoking abstinence.Therefore, unadjusted differences between the intervention and control groups in smoking abstinence were assessed using χ 2 tests or the Fisher's exact test.Differences between the intervention and control groups on variables related to smoking behavior were assessed using linear regression analyses and corrected for heaviness of smoking, education level, sex, and age.Longitudinal differences in average scores on psychosocial mediators were tested using linear mixed model analysis with group, time, and group*time as fixed factors, where a random intercept and random slope were included to account for the correlations between repeated measures.For the random part, three options were considered: random intercept only, a random intercept and slope with variance components, or unstructured covariance structure.The results are presented for the one with the lowest Bayesian information criterion (BIC).To account for multiple testing, the significance level was lowered to 0.01, using the Bonferroni correction based on the main question addressing which elements of the Stoptober House (self-efficacy, social norm, attitude, social support, and social pressure) helped participants stay abstinent.This adjustment implies that p values ≤0.01 were considered statistically significant.Independent-samples t tests or χ 2 tests were used to test for differences between the intervention and control groups and between participants who completed all questionnaires and those who did not (non-response analyses).

Qualitative Interviews and Analyses
On the fourth and fifth days of the intervention, we conducted semi-structured qualitative interviews (one interview per participant) to gain a deeper insight into the participants' experiences with the Stoptober House.We interviewed the participants about their experiences in the Stoptober House.This included questions about which aspects of the program had been most beneficial to them, their experiences with the smoking cessation counselors, whether they had successfully quit smoking, and their plans for maintaining their quit attempt upon returning home (see online suppl.File 1; for all online suppl.material, see https://doi.org/10.1159/000537929 for the topic list).We interviewed 16 participants: 11 women and five men; their ages ranged from 30 to 70 years.The interviews lasted between 16 and 35 min and were conducted by four different interviewers (authors Thomas Martinelli and Gert-Jan Meerkerk and interviewers A and B) for practical reasons.The interviews were audio-recorded and transcribed verbatim.The transcripts were uploaded into NVivo 12.After listening to the audio recordings and reading the transcripts, authors Floor A. van den Brand and Charlotte I. de Haan-Bouma independently coded the transcripts using open inductive coding.After the first three transcripts, codes were compared, and an initial coding framework was agreed upon.After coding seven more interviews, the coding Stoptober House Smoking Cessation Intervention framework was further expanded after consultation between authors Floor A. van den Brand and Charlotte I. de Haan-Bouma.This framework was used to code the remaining interviews and was also retroactively applied to the initial ten interviews.Disagreements about coding were discussed until consensus was reached.The coded data were organized into themes (online suppl.File 2).For the analysis, we focused on elements of the Stoptober House that the interviewees said had helped them quit smoking.The main three themes that we identified in the data were (1) being confined to a smoke-free environment, (2) the smoking cessation counseling, and (3) social support from other quitters in the Stoptober House.

Participants
A total of 115 respondents were included in the current study, of whom 48 participated in the Stoptober House and 67 registered for the Stoptober House but were not selected to participate (Table 1).On average, participants in the intervention group were younger than those in the control group, more often of male sex, and were more confident in their ability to remain abstinent during Stoptober.In the intervention group, 38/48 (79%) and, in the control group, 22/67 (33%) of the respondents completed all questionnaires.Compared to participants who completed all questionnaires (n = 60), participants who did not complete all questionnaires (n = 55) were more likely to be from the control group and were more determined to quit smoking, but did not differ significantly in age, sex, education level, heaviness of smoking, previous quit attempts, motivation, or confidence to quit smoking.

Smoking Abstinence
As smoking was not allowed in the Stoptober House, all 48 participants in the intervention group necessarily made a quit attempt.In the control group, 34 out of 67 participants completed the questionnaire directly after the Stoptober House ended (T1).Of these participants, 17 out of 34 (50%) reported having made a quit attempt (Fig. 1; online suppl.file 3).At T1, 40 out of 48 participants (83.3%) in the intervention group and eight out of 67 participants (11.9%) in the control group reported to have quit smoking (p < 0.001).Eight weeks after the Stoptober House ended (T3), the difference was still statistically significant with 24 (50.0%)participants in the intervention group being abstinent from smoking compared to five (7.5%) in the control group (p < 0.001).
When only participants who reported making a quit attempt were selected for the analysis, at T3, 22 out of 38 participants (57.9%) in the intervention group were abstinent from smoking compared to four out of 17 participants (23.5%) in the control group (p = 0.022).

Psychosocial Mediators
Estimated marginal mean scores on the psychosocial mediators are presented in Figures 2 and 3.The linear mixed model analyses showed that after correcting for baseline score, self-efficacy was significantly higher in the intervention group than in the control group for T1-T3 (online suppl.file 4).Mean attitude scores were high in both groups and were not significantly different between the intervention and control groups after correction for baseline score.Social support was significantly higher in the intervention group directly after the Stoptober House but did not differ significantly between groups at later time points.Analyses showed no significant differences between the groups in social norm and social pressure.

Perceived Active Elements of the Stoptober House
All participants in the intervention group reported at T1 that the Stoptober House had helped them a lot to quit smoking.In the intervention group, 79.2% reported that Stoptober helped them a lot to quit smoking, compared to 13.4% of the control group (p < 0.001).Stoptober House participants were less likely to be exposed to cues that induced craving (p = 0.001) and reported that it was more difficult to obtain cigarettes (p = 0.005) compared to the control group (Table 2).The most frequently cited reasons for registering at the Stoptober House were the coaching sessions (selected by 83.3%, online suppl.file 5) and quitting with others (selected by 70.8%).Notably, a different environment, no cigarettes available, and lack of smoking cues were mentioned by only 45.8%, 37.5%, and 29.2% of participants before the Stoptober House, respectively, but received relatively high scores as contributing to quitting smoking (mean scores between 4.5 and 4.7 out of 5) after the Stoptober House.
Results from Qualitative Interviews: What Helped Stoptober House Participants to Quit Smoking?Many interviewees said that the Stoptober House had made it easier to quit smoking."I actually expected that it would cost me a lot of effort that I would get cranky and   according to the interviewees, were being confined to a smoke-free environment, the smoking cessation counseling, and social support from other quitters in the Stoptober House.These three perceived active elements are described below.
Being "Locked Up" in a Smoke-Free Environment Because the interviewees agreed that they would not leave the smoke-free Stoptober House, it was impossible for them to get cigarettes from another person or to buy cigarettes in the shop.Interviewees mentioned that the unavailability of cigarettes and the inability to buy them protected them from potential relapse when they felt the urge to smoke: "Because we're locked up here and there's no access to cigarettes, that's the main thing.If I had tried it at home, I would have started again within an hour."(participant 5, man, 30 years old).It also helped to be in a different environment, because at home, interviewees were easily tempted to smoke: "If I had been at home and had quit, then there only has to be one setback. . .Or if I watch football. . .Then I already know.Those are my triggers."(participant 14, woman, 64 years old).For some, the Stoptober House provided a safe environment to practice with specific triggers, such as drinking alcohol, without the risk of relapse: "Here you can experience: "I take a sip of beer and I immediately think of my fag." (. ..)Here I can get used to it."(participant 5, man, 30 years old).Some interviewees mentioned that staying at the Stoptober House helped them to fully focus on the quitting process because they were relieved from work commitments and did not have to think about other responsibilities in their daily lives: "You're not busy with your work, or whatever.You just have some time to yourself to get it all started."(participant 10, woman, 38 years old).The full-day program with various activities distracted interviewees from their cravings to smoke.Many interviewees said that their motivation for participating in the Stoptober House was to get through the first difficult days of quitting smoking and to be well prepared to continue their quit attempt when they went home: "I think it's a kick start.My biggest problem often lies in that first week.That first week (. ..) is not a problem now because (smoking) is not allowed here."(participant 7, woman, 46 years old).By signing up for the Stoptober House, participants made a commitment to quit smoking.One interviewee said that what helped him the most was "Having to do it (quit smoking) because you are taking that step.You commit to the fact that there is no smoking and that you are quitting and you take it seriously."(participant 12, man, 58 years old).

Smoking Cessation Counseling
Many interviewees were very positive about the professional expertise of the smoking cessation counselors.During the counseling sessions, the interviewees increased their knowledge about the health consequences of smoking, gained more insight into the mechanisms of their addiction and received practical tips for staying abstinent: "They have quite a lot of wisdom and tips.And again, what works for one person may not work for another.But at least now you get enough that you can do something with."(participant 3, man, 36 years old).The counseling increased the self-efficacy of some participants.Having demonstrated to themselves that they could refrain from smoking for 5 days, and because they had received training and tools, participants felt more confident in their ability to sustain abstinence beyond their stay in the Stoptober House.One participant stated "I'm being trained in such a way that I'm very confident that I'll be successful in 6 months."(participant 7, woman, 46 years old).Some participants said they would have preferred talking less about smoking because it triggered cravings: "If there are only people who say, 'don't smoke, don't smoke, don't smoke,' then you're thinking about it."(participant 5, man, 30 years old).The counselors were considered competent, approachable, good listeners, and genuinely involved with the participants.Some participants found it an added value that counselors had once been smoking themselves.
Counselors who talked about their own experience with smoking cessation, had experienced relapse, and knew how difficult it could be to quit smoking were regarded as more credible and understanding by certain participants: "If someone speaks from their own experience, it is better than saying, 'I've never smoked, but I'll tell you how not to do that anymore.'"(participant 3, man, 36 years old).The proactive approach of the counselors and the fact that they took into account the individual needs of the interviewees were praised.The interviewees also appreciated that the counselors were not only present during the daily group counseling sessions, but were also available throughout the day for individual counseling when interviewees were struggling.One interviewee said, "They (counselors) are very good.You can go to them whenever you want.If you have any questions, they are there for you.And they do these coaching sessions very well too.They listen to you." (participant 1, woman, 50 years old).Furthermore, participants valued the proactive approach of the counselors, who consistently initiated contact, inquiring about the participants' well-being, and extending support when they observed a participant going through a challenging moment.
Social Support from Other Quitters The majority of the interviewees described how the social support of other quitters in the Stoptober House made their quit attempt easier.They were able to share their experiences with others with the same goal and similar difficulties in quitting smoking.One participant said, "You do have support from each other, you are all in the same boat.You have the same feelings, the same irritations, the same cravings."(participant 9, woman, 49 years old).Another person said, "When you see that someone is having a hard time, there is always someone who comes to support you.And you yourself support someone else.Yes, you are like a kind of family to each other.I really like that."(participant 1, woman, 50 years old).Because the interviewees had the same goal to quit smoking and stayed in the same house day and night, they quickly bonded with each other.Some interviewees also experienced social pressure from the group to complete their stay in the House: "If I'd had the urge to go home and I'd been the first and I had to pass 49 other people, like "Yeah guys, I'm going to give up. ..", that's a little disappointing."(participant 3, man, 36 years old).A few interviewees mentioned that they were not comfortable being in a large group with others all the time."I have a huge aversion to groups, so I find that horrifying."(participant 7, woman, 46 years old).Some interviewees said that a disadvantage of the group setting was that certain people in the House annoyed them.

Discussion
The aim of the present pilot study was to explore whether participation in the Stoptober House increases smoking cessation success and to assess which elements of the Stoptober House helped participants remain abstinent.Our results show that half of the Stoptober House participants were successful in quitting smoking up to 8 weeks after the end of the Stoptober House.A review of 14 studies on residential treatment for tobacco use reported continuous abstinence rates at 6 or 12 months ranging from 52% to 29%.However, it is important to note that, comparable to the present research, many of these studies had limitations, such as the absence of randomization or a control group, and a lack of biochemical verification for abstinence.
The 8-week abstinence rate of 50% that was observed in the present study is relatively high compared to other smoking cessation interventions [24,25].More specifically, a modeling study on pharmacological treatment suggests that 8-week abstinence rates are approximately 25% for nicotine replacement therapy and bupropion and around 45% for varenicline [24].Another study involving high-intensity telephone counseling for heavy smokers showed an abstinence rate of 23% at 2 months [25].All Stoptober House participants were trying to quit when they entered the house.This commitment may have contributed significantly to the sustained higher quit rates compared to Stoptober participants at home, of whom only 50% reported having made a quit attempt and who were also less successful in remaining abstinent compared to the intervention group.Nevertheless, it is important to consider that a considerable number of participants from the control group were lost to follow-up.Due to the lack of information on the cessation success rate of these individuals, the assumptions in the analyses may underestimate the true rates.However, comparing the percentage of abstinent smokers among the control group individuals who made a quit attempt (23.5%) with findings from previous studies that modeled the relapse curve reveals comparable results [14,24].
The qualitative interviews revealed three important active elements of the Stoptober House, according to participants: the smoke-free environment, smoking cessation counseling, and social support.Significantly, these elements align with the key working mechanisms identified in a recent review of residential treatment for tobacco use [13].The Stoptober House setting was seen as an active element by interviewees.In this smoke-free environment, they reported that they were less likely to be exposed to smoking cues, which can increase cravings and can act as triggers for smoking behavior [26][27][28].In addition, agreeing not to leave the house prevented participants from making impulse purchases when they felt the urge to smoke and thus potential relapse.Our findings suggest that individuals may underestimate environmental influences (e.g., smoking cues, availability of cigarettes) on their smoking behavior and smoking cessation success.Therefore, the importance of creating an environment that is conducive to smoking abstinence should be more strongly emphasized in smoking cessation treatments and in media campaigns.
The Stoptober House participants experienced a higher level of social support during their stay in the house than people from the control group who participated in Stoptober from home.The feeling of quitting together with peers and the social pressure to complete the stay in the Stoptober House was perceived as an important active element.This finding is supported by previous research showing the effectiveness of smoking cessation programs that provide social (peer) support, such as group behavioral therapy [4,29,30]."Quitting with others" was the second most frequently cited motivation in the questionnaires for participating in the Stoptober House.Therefore, it is important to provide and promote treatment programs with a social component for people who lack support for quitting smoking in their own environment.
A final important active element of the program, according to the respondents, was the coaching provided in the Stoptober House.The combination of the group counseling sessions with the possibility to receive individual support directly from the coaches when needed was highly appre-ciated.The availability of the smoking cessation coaches throughout the day distinguishes the Stoptober House program from standard treatment programs with prearranged appointments.This suggests that for people with high nicotine dependence, a combination of group training and proactive individual counseling may be a promising approach to smoking cessation treatment.
With an average daily consumption of 20 cigarettes, participants in the current study were heavy smokers compared to the Dutch population, where the average daily consumption in 2019 was 10 cigarettes and of which only 14% of people who smoked reported to smoke 20 or more cigarettes per day [31].In addition, more than 90% of people in our study reported a previous quit attempt, compared to 65% of the Dutch population [32].The Stoptober House was positively evaluated by individuals with a high nicotine dependence level and showed promising short-term results regarding smoking abstinence.Because people with high nicotine dependence may benefit from more intensive treatment, it should be further investigated whether such a residential smoking cessation treatment program can benefit this group.Some observational studies have found high abstinence rates after residential treatment programs for people who smoke heavily [9,11,33], but randomized controlled trials are needed to provide more certainty about these results.Future research also needs to assess whether this type of intervention is cost-effective, to inform policy makers about whether it should be made structurally available as a treatment option.

Limitations
The current study has limitations, and thus the results should be interpreted with caution.The study samples compared were not randomized, and the background characteristics of sex and age differed between the intervention and control groups.In addition, loss to followup was particularly high in the control group, which may make the comparison with the control group possibly unreliable.Smoking abstinence in the current study was based on self-report but should ideally be biochemically validated [34].Furthermore, due to the small number of successful quitters in the control group, we were not able to correct for potentially influential background characteristics of the participants by using covariates in all analyses.Finally, our follow-up period of 8 weeks was relatively short.Further research should investigate whether the relatively high quit rates in the intervention group are maintained in the long term.

Conclusions
The current pilot study suggests that the 5-day Stoptober House intervention helped half of the participants to quit smoking for at least 8 weeks.The active elements of the intervention, according to the participants, were the lack of opportunity to smoke, the all-day availability of smoking cessation counselors, and the social support from peers.These findings highlight the contribution of environmental and social influences to smoking cessation success and suggest that residential smoking cessation support may be a promising form of intervention for certain groups of people who smoke.Further research is needed to confirm (or replicate) the effects found and to determine whether this type of intervention is cost-effective in the long term and whether it should be included in tobacco dependence treatment guidelines.

Fig. 1 .
Fig. 1.Percentage and 95% confidence interval of participants abstinent from smoking in the intervention and control groups at various time points.*p < 0.001.

Fig. 2 .
Fig. 2. Estimated marginal means of selfefficacy, social norm, and attitude for intervention (Int) and control (Con) groups at various time points.Linear mixed model analyses with a random intercept on participant level.

Fig. 3 .
Fig. 3.Estimated marginal means of social support and social pressure for intervention (Int) and control (Con) groups at various time points.Linear mixed model analyses with a random intercept on participant level.

Table 2 .
Linear regression analysis assessing the effect of the Stoptober House intervention on variables related to smoking at T1 "Last questionnaire" refers to T0 measurement.Multiple regression analyses corrected for HSI, education level, sex, and age.
*a Intervention versus control group.