Assignment Respond to this prompt following rubric guidelines as posted: 1. State your overall appraisal of this article (include/exclude/seek further info) and provide a rationale of ~2-3 p

Effectiveness and Cost-Effectiveness of Repeated Implementation Intention Formation on Adolescent Smoking Initiation: A Cluster Randomized

Controlled Trial

Mark Conner University of Leeds

Sarah Grogan Manchester Metropolitan University

Robert West and Ruth Simms-Ellis University of Leeds

Keira Scholtens Staffordshire University

Bianca Sykes-Muskett University of Leeds

Lisa Cowap Staffordshire University

Rebecca Lawton University of Leeds

Christopher J. Armitage University of Manchester

David Meads University of Leeds

Laetitia Schmitt University of York

Carole Torgerson Durham University

Kamran Siddiqi University of York

Objective: Forming implementation intentions (if–then plans) about how to refuse cigarette offers plus antismoking messages was tested for reducing adolescent smoking. Method: Cluster randomized con- trolled trial with schools randomized (1:1) to receive implementation intention intervention and messages targeting not smoking (intervention) or completing homework (control). Adolescents (11–12 years at baseline) formed implementation intentions and read messages on 8 occasions over 4 years meaning masking treatment allocation was not possible. Outcomes were: follow-up (48 months) ever smoking, any smoking in last 30 days, regular smoking, and breath carbon monoxide levels. Analyses excluded baseline ever smokers, controlled for clustering by schools and examined effects of controlling for demographic variables. Economic evaluation (incremental cost effectiveness ratio; ICER) was con- ducted. Trial is registered (ISRCTN27596806). Results: Schools were randomly allocated (September– October 2012) to intervention (n � 25) or control (n � 23). At follow-up, among 6,155 baseline never smokers from 45 retained schools, ever smoking was significantly lower (RR � 0.83, 95% CI [0.71, 0.97], p � .016) in intervention (29.3%) compared with control (35.8%) and remained so controlling for demographics. Similar patterns observed for any smoking in last 30 days. Less consistent effects were observed for regular smoking and breath carbon monoxide levels. Economic analysis yielded an ICER of $134 per ever smoker avoided at age 15–16 years. Conclusions: This pragmatic trial supports the use

This article was published Online First March 7, 2019. Mark Conner, School of Psychology, University of Leeds; Sarah Gro-

gan, Department of Psychology, Manchester Metropolitan University; Robert West, Institute of Health Sciences, University of Leeds; Ruth Simms-Ellis, School of Psychology, University of Leeds; Keira Scholtens, Faculty of Health Sciences, Staffordshire University; Bianca Sykes- Muskett, School of Psychology, University of Leeds; Lisa Cowap, Faculty of Health Sciences, Staffordshire University; Rebecca Lawton, School of Psychology, University of Leeds; Christopher J. Armitage, Manchester Centre for Health Psychology, University of Manchester; David Meads, Institute of Health Sciences, University of Leeds; Laetitia Schmitt, Centre for Health Economics, University of York; Carole Torgerson, School of Education, Durham University; Kamran Siddiqi, Department of Health Sciences, University of York.

This research was supported by a grant (MR/J000264/1) from the United Kingdom Medical Research Council/ National Prevention Research Initiative. Christopher J. Armitage is also supported by the NIHR Manchester Biomed- ical Research Centre.

This article has been published under the terms of the Creative Com- mons Attribution License (http://creativecommons.org/licenses/by/3.0/), which permits unrestricted use, distribution, and reproduction in any me- dium, provided the original author and source are credited. Copyright for this article is retained by the author(s). Author(s) grant(s) the American Psychological Association the exclusive right to publish the article and identify itself as the original publisher.

Correspondence concerning this article should be addressed to Mark Conner, School of Psychology, University of Leeds, Leeds LS2 9JT, United Kingdom. E-mail: [email protected]

Journal of Consulting and Clinical Psychology © 2019 The Author(s) 2019, Vol. 87, No. 5, 422–432 0022-006X/19/$12.00 http://dx.doi.org/10.1037/ccp0000387

422

of repeated implementation intentions about how to refuse the offer of a cigarette plus antismoking messages as an effective and cost-effective intervention to reduce smoking initiation in adolescents.

What is the public health significance of this article? This study suggests that getting adolescents to read anti-smoking messages and form implementation intentions about how to refuse the offer of a cigarette in classroom time reduces smoking initiation. Such a classroom-based intervention is an effective and cost-effective way to reduce smoking initiation in adolescents and is readily scalable.

Keywords: smoking initiation, adolescents, implementation intentions, smoking prevention

Supplemental materials: http://dx.doi.org/10.1037/ccp0000387.supp

Tobacco smoking continues to be an important cause of mor- bidity and mortality, particularly later in life (Gowing et al., 2015). Most smokers initiate the habit as adolescents (McRobbie, Bullen, Hartmann-Boyce, & Hajek, 2014; Polosa, Rodu, Caponnetto, Maglia, & Raciti, 2013; Singh et al., 2016) with around 40% of adult smokers having started before they reached 15 or 16 years of age (Warner, 2016). Although quitting smoking at any age is beneficial, maximum health benefit accrues from never initiating smoking. Addiction to nicotine can be established rapidly in ado- lescence (DiFranza et al., 2007) with strong associations between having a first cigarette (Sargent, Gabrielli, Budney, Soneji, & Wills, 2017) or smoking as infrequently as 1 day in the past month (Saddleson et al., 2016) and progression to regular smoking as an adult. Additionally, early uptake of smoking is associated with more cigarettes smoked (Chassin, Presson, Pitts, & Sherman, 2000; Taioli & Wynder, 1991) and lower quit rates (Ferguson, Bauld, Chesterman, & Judge, 2005) in adulthood. These findings point to the potential value of effective interventions to reduce smoking initiation and avoiding that first cigarette in adolescents. The present article reports a pragmatic trial of an intervention designed to reduce smoking initiation in adolescents by targeting the refusal of offers of a cigarette.

The current intervention was based on implementation inten- tions. Implementation intentions are specific “if–then” plans (Goll- witzer, 1993). Gollwitzer (1993, 1999) defined an implementation intention as a plan of how, where, and when to perform a behavior. This type of plan establishes a link between a critical situation and a planned behavior (“If I encounter Situation X then I will do Y”). Through forming an implementation intention, it has been argued that an individual passes control of goal directed activities from the self to critical situations (e.g., Aarts, Dijksterhuis, & Midden, 1999). The critical situation when encountered then prompts the intended behavior, through automatic activation of the plan (see Webb & Sheeran, 2003). In this way implementation intentions facilitate quick and reliable initiation of the intended behavior by increasing readiness to respond to specified opportunities (when “X” occurs; Gollwitzer, 1993).

Implementation intentions have been found to be effective means to change a range of behaviors (Gollwitzer & Sheeran, 2006), including promoting smoking cessation (Armitage, 2016). Empirical findings indicate that the effects of forming implemen- tation intentions are often contingent on the presence of strong motivation or goal intention to perform the behavior (e.g., Prest-

wich, Sheeran, Webb, & Gollwitzer, 2015; Sheeran, Webb, & Gollwitzer, 2005). A number of studies (including the present one) therefore use interventions that combine the formation of imple- mentation intentions with the presence of motivational messages about the target behavior (e.g., Prestwich, Lawton, & Conner, 2003).

Two previous studies tested implementation intentions in conjunction with antismoking messages in relation to smoking initiation in adolescents. In a pilot study, Higgins and Conner (2003) tested the effects of engaging with antismoking mes- sages plus forming a single implementation intention on self- reported ever-smoking 2 months later. Implementation inten- tions were formed in relation to refusing offers of a cigarette (intervention; e.g., If offered a cigarette then I will say “no thanks, I do not smoke”) or completing homework (control). Of the 104 baseline never smokers, 0% initiated smoking in the intervention group, while 6% initiated smoking in the control group. In a later explanatory trial with 1,338 adolescents, Con- ner and Higgins (2010) tested the effects of forming implemen- tation intentions on how to refuse the offer of a cigarette after engaging with antismoking messages on eight occasions (inter- vention). The control conditions also included engaging with antismoking messages on eight occasions plus an intervention designed to promote self-efficacy not to smoke, or forming implementation intentions about completing homework or pro- moting self-efficacy to complete homework. Compared with the combined control conditions, the intervention was shown to reduce self-reported smoking and breath carbon monoxide lev- els significantly at 4 years postbaseline.

The present research was designed as a pragmatic cluster randomized controlled trial of the effectiveness of forming repeated implementation intentions about how to refuse an offer of a cigarette after engaging with antismoking messages com- pared to usual practice on tobacco control. Previous studies (Conner & Higgins, 2010; Higgins & Conner, 2003) showed the efficacy of combining implementation intentions with anti- smoking messages compared with antismoking messages alone. Therefore, this pragmatic trial compared the combined inter- vention with a control condition using the same intervention techniques (i.e., implementation intentions combined with per- suasive messages) but focusing on a distinct behavior (com- pleting homework) rather than, for example, comparison with antismoking messages alone. In the control condition used here

423IMPLEMENTATION INTENTIONS AND ADOLESCENT SMOKING

adolescents formed repeated implementation intentions about how to complete homework after engaging with prohomework messages.

This present intervention (i.e., forming repeated implementation intentions on how to refuse the offer of a cigarette after engaging with antismoking messages), if shown to be effective in a prag- matic trial, could be deployed across schools to reach the majority of adolescents in order to tackle smoking initiation in this age group. In addition, this intervention is relatively low cost, requiring only 30–50 min per session for teachers to implement in classroom time (including engaging with antismoking messages and complet- ing an implementation intention questionnaire; Conner & Higgins, 2010; Higgins & Conner, 2003). This contrasts with other anti- smoking interventions tested in this age group that tend either to have only mixed evidence for their effectiveness (for reviews see MacArthur, Harrison, Caldwell, Hickman, & Campbell, 2016; Thomas, McLellan, & Perera, 2015; Wiehe, Garrison, Christakis, Ebel, & Rivara, 2005), or have effectiveness evidence but are high cost (Campbell et al., 2008; Peterson, Kealey, Mann, Marek, & Sarason, 2000).

Method

Study Design and Participants

Secondary schools in two areas of England (Leeds and Stafford- shire Local Education Authorities) were eligible for inclusion in the study. Head teachers provided written consent that their schools would participate in the trial and continue usual smoking education and policies on tobacco control for the trial duration. Schools sought parental consent (i.e., passive consent) by writing to parents of pupils in the relevant year group (Year 7 at baseline, 11- to 12-year-olds). Very few parents asked for their child to be excluded from data collection sessions. All adolescents in the relevant year group were eligible for participation. Adolescents provided active assent by completing questionnaires. As passive consent was used, ethical/governance procedures required that adolescent data be collected anonymously and so matching of data across time points was based on individually generated codes.

The University of Leeds (School of Psychology, Faculty of Medicine and Health) ethical review committee approved the study (reference 12–0155 on September 24, 2012). The study was registered on October 26, 2012 (ISRCTN27596806) before any intervention sessions. There were no changes to the methods after trial commencement. Details of the trial protocol have been pub- lished previously (Conner et al., 2013).

Randomization and Masking

School was the unit of randomization. Schools were randomized by random number generator to intervention or control conditions on a 1:1 ratio by the trial statistician (RW). Randomization took place before recruitment of participants within each school. Due to the nature of the intervention, adolescents, teachers administering the intervention, heads of school, and data collection assistants were aware of group allocation. The trial statistician who con- ducted the analyses was initially blinded to condition.

Procedures

Self-reported data were collected at baseline plus 12, 24, 36, and 48 months postbaseline by research staff (present to answer ques- tions) via questionnaire in groups (classes or year group assem- blies) with adolescents requested not to confer. At each time point a smokerlyzer measure of breath carbon monoxide levels was taken individually with readings not available to adolescents.

The eight intervention sessions took place separately to data col- lection in classroom time (with each session containing approximately 26 adolescents) approximately every 6 months starting within 2 months of baseline data collection and were each led by a teacher. The content of sessions was designed to be matched (in relation to duration and frequency plus the use of written motivational materials and an implementation intention formation task) across the two con- ditions but focusing on smoking (intervention condition) or complet- ing homework (control condition) as an unrelated behavior. Adoles- cents engaged with motivational materials (read antismoking messages or prohomework messages plus engaged in related tasks designed to increase engagement with the messages) and then com- pleted implementation intentions sheets in relation to the target be- havior (not smoking in intervention condition; completing homework in control condition). The target behavior in the control condition (completing homework) was selected to be a nonhealth related be- havior appropriate for adolescents. The interventions were designed to run within a standard classroom session (50 min) with the majority (60%) of the time devoted to the messages.

Implementation intention formation was consistent across inter- vention sessions. Adolescents were first required to tick an option to indicate how they could refuse smoking this school term (“Tick ONE of the following things you could say if you were offered a cigarette or if you were tempted to smoke . . .; No thanks, smoking makes you smell awful; No, I do not want yellow teeth; No, I do not want to get addicted; No thanks, if you’re buying cigarettes you’re buying cancer; No it’s really bad for my asthma”). They were then requested to write in the selected response or generate a new response of their own to complete a statement (“If someone offers me a cigarette, then I will say . . .; e.g., No cancer sticks for me”). Adolescents were then required to indicate where they would not smoke (“Tick ALL the places where you will not smoke: I will not smoke at school; I will not smoke at home; I will not smoke at a party; I will not smoke with my friends; I will not smoke if I’m offered a cigarette”) and to respond to a question about smoking this school term (“I think I can make sure I do not smoke this term: yes, no”). The task was similar in the control condition but completed in relation to completing homework. Participants completed the implementation intention task individ- ually by ticking boxes and writing down responses. The imple- mentation intention sheets were collected in by the teacher and returned to the research team.

The motivational materials provided antismoking or prohome- work messages and were paper based. The motivational materials were different in each session (i.e., eight sets of materials), were all judged to be age-appropriate by an experienced school teacher, and were similar in content to that used in our previous work (Conner & Higgins, 2010; Higgins & Conner, 2003). For example, the first set of antismoking materials (“Smoking: It’s not worth it”) focused on 10 reasons not to smoke and included text and pictures along with a quiz designed to promote engagement with the materials.

424 CONNER ET AL.

Full copies of the implementation intention sheets and motiva- tional materials can be obtained from the first author.

Training sessions were run with teachers in each year of the study. These were 45-min sessions run in each school that focused on the broad purpose of the intervention and details of the inter- vention content (motivational messages and implementation inten- tion sheets plus a plan of how to run the session). An opportunity to discuss the content and any potential problems with delivery was provided. The need to stick to the planned content and ensure all implementation intention sheets were fully completed was emphasized. A teacher in each school acted as a coordinator and monitored the delivery of all sessions and was available to answer teachers’ questions.

Outcome Measures

Four measures of smoking were used as outcomes at the 48-month follow-up. Self-reported cigarette use was assessed at each time point using a standardized measure (Office for National Statistics, 1997); adolescents ticked one of: (a) I have never smoked; (b) I have only tried smoking once; (c) I used to smoke sometimes, but I never smoke cigarettes now; (d) I sometimes smoke cigarettes now, but I do not smoke as many as one a week; (e) I usually smoke between one and six cigarettes a week; (f) I usually smoke more than six cigarettes a week. This was used to create our first two measures of smoking: ever smoking (ticking response a coded 0; ticking responses b–f coded 1); regular smoking (ticking responses a–d coded 0; ticking responses e–f coded 1).

Any smoking (last 30 days) was assessed at 48-month postbase- line only (self-reported number of days in last 30 days using each of cigarettes, cigars, pipes, or sheesha/hookah was recorded and summed). Any smoking (last 30 days; 0 days coded 0; �1 day coded 1) was our third smoking measure.

Breath carbon monoxide (CO) levels (in parts per million; COppm) were assessed using the Micro � Smokerlyzer® CO Monitor (Bedfont Scientific Limited, Kent, United Kingdom) at each time point. However, the short half-life (four-six hours) of breath CO means that such measures are only reliable and valid for assessing recent cigarette smoking (Bedfont, 2017; Jarvis, Tunstall-Pedoe, Feyerabend, Vesey, & Saloojee, 1987; Stookey, Katz, Olson, Drook, & Cohen, 1987). A variety of cut-offs have been used in the literature to indicate smoking in adults. We used the cut-off recommended by the device manufacturer as a clear indication of recent smoking in adolescents (�6 ppm CO coded as 0; �6 ppm CO coded as 1). Breath CO �6 ppm was our fourth smoking outcome measure.

For the three smoking measures taken at each time point (ever smoking, regular smoking, breath CO �6 ppm) we also created measures of smoking across Time Points 2 to 5 (based on being categorized as smoking on a measure on at least one of the time points).

Other Measures

Other measures were assessed as covariates and/or moderators and measured at 48 months follow-up. At the school level we recorded geographical area (Leeds; Staffordshire) and size (num- ber of pupils), and area level socioeconomic status (percentage of pupils in a school receiving free school meals; Croxford, 2000). At

the individual level we assessed gender, ethnicity (self-reported classification dichotomized into non-White vs. White) and individual-level socioeconomic status (four-item Family Affluence Scale [FAS] scored 0–9 with higher scores indicating greater affluence; Boyce, Torsheim, Currie, & Zambon, 2006).

Fidelity checks assessed adherence, quality of delivery, and exposure to the intervention. The study coordinator in each school was requested to monitor adherence and provide feedback on the number of intervention sessions in their school not run as planned. Teachers were requested to return to the study coordinator com- pleted implementation intention sheets after each session. These were subsequently collected from each school. For approximately half of these sessions, teachers were also requested to complete feedback sheets on session delivery. The feedback sheets included a rating of how well the session went (“The lesson went incredibly well;” strongly disagree, disagree, neither agree nor disagree, agree, strongly agree). Quality of delivery was also assessed in observation of sessions by researchers. Approximately 7% of sessions were observed by researchers, including at least one session in each school. Observation sheets included a rating of overall quality of delivery (“Overall session quality was . . .;” low, moderate, satisfactory, good, high). Exposure to the intervention was assessed by self-reported questions from participants at the final follow-up. Those in the intervention (antismoking) condition were asked to indicate which sessions they attended by checking a box next to each session (identified by number, short title, and image of the antismoking information) to give a score between 0 and 8. All participants were requested to indicate if they had moved school since the beginning of the study and to specify the old school and year of change (coded into total numbers changing school, numbers moving between schools in different conditions, numbers moving from nonstudy schools or nonspecified schools).

Data relevant to costing the intervention fully were also col- lected. A number of other measures were taken but are not reported here (full details available from first author along with intervention materials, analysis scripts, and raw data).

Statistical Analyses

Based on a power of 90% to detect a 5% difference in smoking rates, an intraclass correlation (ICC) of .01, and alpha of .05, prior sample size calculations indicated the need for at least 3,672 adolescents from 36 schools in the analyses (Conner et al., 2013). We first summarized the measures taken for the full sample and the intervention and control conditions. The main analyses tested for differences between the intervention and control conditions at 48-month postbaseline in each of the four smoking measures among those who were self-reported never smokers at baseline. Those who self-reported ever smoking at baseline (N � 301) were removed from all analyses. The largest amount of missing data was for baseline ever smoking, principally due to a failure to match individually generated codes. Missing self-reported ever smoking at baseline was imputed to be zero (i.e., never smoking). Missing data from other variables ranged from 0.2% for gender to 5.8% for any smoking (in last 30 days; see Table 1 for details of numbers of missing data points for each variable) and only 88% of the 6,115 never smokers in the sample would have been available for anal- ysis under the traditional listwise deletion method across these variables. Data were primarily missing due to item nonresponse.

425IMPLEMENTATION INTENTIONS AND ADOLESCENT SMOKING

We addressed the problem of missing data through multiple im- putation using chained equations (MICE; van Buuren & Groothuis-Oudshoorn, 2011) after confirming that the missing values were missing at random. The mice command in R was used to generate 20 imputed data sets that were analyzed using the pooled command. Imputed values compared reasonably with ob- served values and the results using listwise deletion were similar to multiple imputation, so imputed results are presented.

Based on the distribution and frequency of outcomes, log bino- mial regressions, implemented in R were used to predict each smoking outcome (ever smoking; any smoking in the last 30 days, regular smoking, breath CO �6 ppm) controlling for the clustering among schools (multilevel modeling). Condition and percentage free school meals were Level 2 variables in these models, while gender, ethnicity, and the FAS scores were Level 1 variables. We report the risk ratio (RR), the 95% confidence interval around the risk ratio (95% CI), and the p value for each predictor variable in these regressions. The RR is the ratio of likelihood of the outcome (in this case smoking) across the compared conditions

(intervention vs. control). For each step we also report the ICC. At Step 1 condition was entered, while at Step 2 we examined the effects of controlling for demographic variables (school SES; boys vs. girls; non-White vs. White ethnicity; individual level of socio- economic status based on FAS). At Step 3 we tested whether each of these demographic variables significantly moderated the effects of the intervention. For outcome measures taken at each of the postbaseline time points (ever smoking, regular smoking, and breath CO �6 ppm), sensitivity analyses assessed intervention effects on smoking on at least one time point (i.e., for each smoking measure an outcome was created: 0 � not smoking at any time point; 1 � smoking at one or more time points). Fidelity analyses also examined whether attending no smoking intervention sessions versus a few or most smoking intervention sessions in- fluenced the key findings. Fidelity analyses also examined whether the key findings were influenced by excluding participants who self-reported changing school.

The economic evaluation was based on the incremental cost of the intervention per averted smoker at age 15–16 years. The

Table 1 Descriptive Data for Sample (Comparison of Control and Intervention Conditions)

Measures Total Control Intervention p1

Baseline School size2 940 (305.9) 878.0 (348.0) 990.2 (264.3) .225 Area

Leeds 20/45 (44.4%) 8/20 (40.0%) 12/25 (48.0%) Staffordshire 25/45 (55.6%) 12/20 (60.0%) 13/25 (52.0%) .764

Free school meals2 16.55 (9.30) 14.97 (6.81) 17.81 (10.87) .313 Baseline self-reported ever smoking

Nonsmoker 4,101/4,402 (93.2%) 1,858/1,967 (94.5%) 2,243/2,435 (92.1%) Ever smoker 301/4,402 (6.8%) 109/1,967 (5.5%) 192/2,435 (7.9%) .002

48-month follow-up (baseline never smokers) Total N 6,155 (100%) 2,719 (100%) 3,436 (100%) Gender

Boys 3,039/6,131 (49.6%) 1,354/2,706 (50.0%) 1,685/3,425 (49.2%) Girls 3,092/6,131 (50.4%) 1,352/2,706 (50.0%) 1,740/3,425 (50.8%) .520 Missing 24 13 11

Ethnicity Non-White 1,038/5,837 (17.8%) 438/2,579 (17.0%) 600/3,258 (18.4%) White 4,799/5,837 (82.2%) 2,141/2,681 (83.0%) 2,658/3,258 (81.6%) .158 Missing 318 140 178

Family affluence scale2 6.24 (1.59) 6.28 (1.57) 6.21 (1.61) .120 Missing 257 113 144

Ever smoking Nonsmoker 4,051/5,974 (67.8%) 1,700/2,648 (64.2%) 2,351/3,326 (70.7%) Ever smoker 1,923/5,974 (32.2%) 948/2,648 (35.8%) 975/3,326 (29.3%) �.001 Missing 181 71 110

Any smoking (last 30 days) Nonsmoker (0 days) 4,843/5,799 (83.5%) 2,075/2,567 (80.8%) 2,768/3,232 (85.6%) Recent smoker (�1 days) 956/5,799 (16.5%) 492/2,567 (19.2%) 464/3,232 (14.4%) �.001 Missing 356 152 204

Regular smoking Nonsmoker 5576/5,974 (93.3%) 2,458/2,648 (92.8%) 3,118/3,326 (93.7%) Regular smoker 398/5,974 (6.7%) 190/2,648 (7.2%) 208/3,326 (6.3%) .159 Missing 181 71 110

Breath CO �6 ppm 5,867/5,951 (98.6%) 2,551/2,599 (98.2%) 3,316/3,352 (98.9%) �6 ppm 84/5,951 (1.4%) 48/2,599 (1.8%) 36/3,352 (1.1%) .014 Missing 204 120 84

1 Difference between intervention and control conditions p-value based on Fisher’s exact test (two-sided). 2 Mean and SD; p-value based on F-test on normalized scores.

426 CONNER ET AL.

costs of implementing the intervention were gathered by re- searchers during the study and expressed in United Kingdom sterling in 2017 prices (converted to U.S. dollars) based on wages and transport costs as at August 2017 provided by the Office for National Statistics. Costs included intervention de- velopment (printing material), delivery (travel and time in- curred in providing training and support), and receipt (teacher time in undertaking training). Costs over the 4-year period were discounted at 3.5% per annum consistent with NICE guidelines (National Institute for Health & Care Excellence, 2018). An incremental cost-effectiveness ratio (ICER) was calculated based on the incremental cost per adolescent of implementing the intervention divided by the difference in the proportion not smoking across conditions.

Results

Sample Description

The study took place between September 2012 and January 2017. A total of 73 s

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