The present study is a 2-arm (telephone counselling versus control condition) randomized controlled trial with three assessments during a period of approximately one year. Participants will be 512 smoking parents and their 9-12 year old children. After giving informed consent and after completing the baseline assessment, 256 parents will be randomly assigned to the telephone counselling condition and 256 parents to the control condition. In the telephone counselling condition, parents will receive up to seven counsellor-initiated telephone calls and three supplementary brochures over a period of approximately three months. In the control condition, parents will receive a standard brochure on smoking cessation. Parent and child assessments will be identical across conditions and take place at baseline, three months after start of the intervention (post-measurement), and twelve months after start of the intervention (follow-up measurement). In both conditions, each parent-child couple will receive an incentive of 100 euro for their participation in all assessments.
Smoking parents will be recruited through their children's primary schools. Primary school boards will be asked to distribute study invitation letters to all children aged 9-12 years and request that children give these letters to their parents. Study invitation letters include information about the study (e.g., purpose of study, length of the study, frequency of assessments, eligibility criteria). Parents will be able to register for the study by returning a form with their contact information in an enclosed envelope. Registration will also be possible via the study website, via e-mail, or via telephone.
Eligibility criteria are stated clearly in the study invitation letter. Inclusion criteria for the present study are: 1) being at least a weekly smoker, 2) being a parent/caretaker of a child in (Dutch) grade 6-8 (9-12 years old), 3) having the intention to quit smoking (currently or in the near future), and 4) giving informed consent. Upon registration, written informed consent of parents will be obtained. The ethics committee of the Faculty of Social Sciences at the Radboud University Nijmegen approved the study's protocol.
Assignment to a group will be performed by a member of the research group who is not involved in the present study. Participants will be stratified by gender, educational level, and smoking intensity (as reported by participants in the baseline questionnaire). If partners who live in the same household participate in the study, randomization will be carried out at household level to avoid contamination between conditions.
Sample size calculation
Based on similar studies, we expected a 6% difference in 7-day point prevalence abstinence rates between the telephone counselling condition and the control condition at 12-months assessment (13% versus 7%, respectively). A statistical power of .80 was targeted. Hypotheses will be tested at a two-sided significance level of .05. The calculated sample size was corrected for participants who will be lost to attrition. Additionally, the sample size was corrected to allow for supplementary analyses of mediation and moderation.
Theoretical basis of the intervention
Telephone counselling will be based on Motivational Interviewing (MI) and cognitive behavioural skill building. MI is considered a client-centered, directive method to enhance intrinsic motivation for behavioural change by exploring and resolving ambivalence . MI's primary goal is to trigger a decision and enhance commitment to this decision, for example by eliciting and selectively reinforcing change talk. MI's empathic, non-confrontational style may be particularly helpful in addressing smokers' ambivalence and defensiveness and in providing a safe counselling environment for smoking parents. When parents express a desire to quit smoking, telephone counselling will shift to cognitive-behavioural skill building. Smokers will be encouraged to create a supportive environment for quitting (e.g., arrange for smoking substitutes, avoid exposure to smoking cues). The overall approach to skill building is a problem-solving one. Smokers are encouraged to identify key barriers to quitting and to remaining quit (e.g., stress, urges and cravings, exposure to smoking cues, dysfunctional cognitions), to identify practical solutions, and to implement and evaluate these solutions. Cognitive-behavioural skill building will also incorporate relapse prevention strategies (e.g., anticipation of difficult situations/lapse to smoking). During telephone counseling, motivation to quit and self-efficacy to quit will be continuously monitored by counsellors. Counsellors will alternate MI and cognitive-behavioural skill building according to the participant's current need for motivation enhancement or skill enhancement.
Telephone counselling condition
In the telephone counselling condition, parents receive proactive telephone counselling based on MI and cognitive-behavioural skill building. Each participant receives up to seven counsellor-initiated phone calls across a period of approximately three months, respectively one 30-minute intake session and up to six additional 10-minute sessions. Telephone counselling will be conducted by professionals of STIVORO (Dutch expert centre for tobacco control). All counsellors are trained and experienced in the delivery of telephone counselling to support smoking cessation. Two different call schedules will be applied to participants who are willing to set a quit date and participants who are not willing to set a quit date.
Participants who are willing to set a quit date
Participants who are willing to set a quit date are offered 1-2 preparatory phone calls before undertaking a quit attempt. During the first phone call, participants are encouraged to set a quit date within 10-12 days. In the following, participants are offered up to six phone calls to support maintenance of smoking cessation. The phone calls focus on the following topics: reasons for smoking and reasons for quitting, nicotine dependence and nicotine withdrawal, craving, coping with difficult situations, weight gain and irritability, and relapse prevention. The first phone call (intake call) will take place approximately 10-12 days before the quit date; the second phone call will take place approximately three days after quit date; the third phone call approximately seven days after quit date; the fourth phone call approximately two weeks after quit date; the fifth phone call approximately four weeks after quit date; the sixth phone call approximately eight weeks after quit date; and the seventh phone call approximately twelve weeks after quit date.
Participants who are not willing to set a quit a date
Participants who are not willing to set a quit date will receive three phone calls. These phone calls are intended to increase the participant's motivation for smoking cessation by use of Motivational Interviewing. During these calls, counsellors aim to explore the participant's reasons for smoking and for quitting, to resolve ambivalence, and to enhance the participant's intrinsic motivation for behavioural change. Participants will receive the second phone call approximately three weeks after the first phone call (intake call). Approximately four weeks later the third phone will be made.
All participants in the telephone counselling condition will receive three supplementary brochures on smoking cessation. All brochures are 4-page, colour-printed, A4-sized booklets which are designed specifically for the present study. The brochures have the following themes: 1) Deciding and preparing, 2) Undertaking a quit attempt, 3) Maintenance of smoking cessation. Each brochure includes additional information about smoking and smoking cessation, tips and exercises, and motivation or self-efficacy enhancing messages. Additionally, each brochure contains information which is relevant to parents (e.g., information about effects of second-hand smoke exposure for children). Participants will receive the first brochure immediately after start of the telephone counselling, the second brochure approximately 2-3 weeks after start of the telephone counselling, and the last brochure approximately 5-6 weeks after start of the telephone counseling.
Participants in the control condition will receive a standard brochure (by STIVORO) on smoking cessation (Stoppen met roken: Willen en kunnen [Quitting smoking: Wanting to quit and being able to quit]). The brochure is a 40-page, colour-printed booklet (size: 12 × 16 centimeters). The brochure will be sent to participants randomized to the control condition within two weeks after baseline assessment. The brochure is divided into 5 parts: information about smoking and smoking cessation, reasons for quitting, tips and exercises, and maintenance of smoking cessation. At the end of the study, telephone counselling will be offered to all participants in the control condition.
An overview of the study design is presented in Figure 1. The baseline measurement will take place between January and July 2011. It is expected that the majority of the questionnaires will be administered digitally (the rest will be administered via mail). The post-measurement will take place approximately three months after start of the intervention. The follow-up assessment follows approximately twelve months after start of the intervention. At all three assessments, questionnaires will be filled in by both the parent and the child. Procedures will be identical across assessments.
In the proposed study, telephone counselling aims to increase cessation rates among smoking parents. The primary outcome measures will be: 1) sustained abstinence between post-measurement and follow-up measurement, 2) 7-day point prevalence abstinence at post-measurement (three months post-intervention) and follow-up measurement (twelve months post-intervention), and 3) 24-hours point prevalence abstinence at post-measurement and follow-up measurement. Additionally, biochemical validation of self-reported smoking cessation will be reported for a random sample (30%) of all study participants who report 7-day point prevalence at follow-up assessment, thereby allowing to estimate the occurrence of over-reporting of abstinence. Secondary outcome measures will include: a 50% reduction in the number of cigarettes smoked per day, occurrence of abstinence of at least 24 hours at some point during the study, implementation of smoking restrictions at home, increase in motivation to quit, use of and adherence to nicotine replacement therapy, number and duration of quit attempts, and change in smoking-related cognitions (e.g., attitudes towards smoking, self-efficacy, social norms). In addition, secondary outcomes will include smoking-related cognitions of children (e.g., attitudes towards smoking, self-efficacy, social norms, intention to smoke) and smoking behaviour of children.
Analyses will be conducted to check whether the randomization has resulted in an equal baseline distribution of relevant participant characteristics across both conditions. In case of group differences at baseline, confounding variables will be included in subsequent analyses. To evaluate smoking cessation rates across groups, we will use logistic regression models. Effect sizes as well as confidence intervals will be reported. To evaluate smoking-related cognitions across groups (in both parents and children), analyses-of-variance and regression analyses will be used. Mediation and moderation will be tested in Mplus. In accordance with the intent-to-treat principle, all participants randomized to a condition will be included in analyses testing of the study hypotheses. In addition, a complete-case analysis will also be conducted, that is, only participants with outcome data on all assessments will be included in the analysis.