Design
Three-pronged, randomized clinical trial in a primary health care setting in Mallorca. We carried out the following: an intensive individual intervention (III) and an intensive group intervention (IGI) as experimental branches, and the standard minimal intervention (MI) as the control branch.
Subjects
The study population was made up of smokers who attended health centres. We established the following inclusion criteria: individuals who smoked and who were in the preparatory phase of smoking cessation in accordance with Prochaska's and Di Clemente's transtheoretical model of health behaviour change [14]. A prepared individual was defined as one who had expressed the wish to quit smoking and who felt ready to set a deadline for doing so not more than one month into the future. Individuals less than 18 years or with terminal illness or certain mental health conditions (dementia and schizophrenia) were excluded.
We expected a smoking cessation rate at 12 months of 5% in the MI, 15% in the III and 25% in the IGI. The sample size needed to detect a 10% difference in the main outcome measure between intervention groups with 5% precision in both directions, 80% power and a 95% confidence level was 199 subjects per intervention group, or 597 in all.
Intervention
Three were conducted: III, IGI and MI. In all three, pharmacological treatment with nicotine derivatives or bupropion was offered as an option at the physician's discretion. Both the III and the IGI consisted of six visits during which the following were provided: counseling, psychological support and standard follow-up. Counseling and psychological support were based on motivational interview techniques [15] that sought to: (a) reinforce in the smoker the motivation to quit smoking before D day (the day fixed for quitting by the smoker) and (b) prevent relapses after smoking cessation. Intensive interventions followed clinical guidelines developed in the Balearic Islands [16, 17]. Physicians and nurses in the III and IGI received identical training on how to implement intensive interventions, whereas health workers in the MI received only the basic training that had been offered previously to all primary health care workers on how to diagnose smoking addiction and provide brief counseling. In all three groups the intervention was carried out by the "microteam," composed of one physician and one nurse. These workers distributed the visits among themselves as they saw fit; all they were instructed to do was to conduct some of the visits together.
Allocation method
An allocation concealment method based on the use of sequentially-numbered, opaque, sealed envelopes was used. All 40 health centers that existed in Mallorca at the time were invited to participate in the study, and 10 agreed. A block of 60 envelopes (20 for III, 20 for IGI and 20 for MI) was prepared in the central research unit for each participating health centre and subsequently sent out.
In each health centre, all physicians and nurses could recruit subjects, but only one "microteam" performed the III, one the IGI and one the MI. Smokers who fulfilled the inclusion and exclusion criteria were invited to participate in the study. If they consented, they were referred to the corresponding physician or nurse, who had them sign the informed consent form. After signing the form, patients picked an envelope at the admissions desk for random allocation to one of the intervention arms. Next, a visit with the doctor or nurse in the intervention arm to which the patient was allocated was scheduled, and the intervention was begun.
Once the intervention had ended, follow-up visits were scheduled at one month, 2 months, 3 months, 6 months, 9 months and 12 months. If a patient missed a follow-up visit, telephone follow-up was attempted. Case recruitment began in March 2005 and finished in June 2006. Case follow-up started in March 2005 and ended in August 2007.
Main outcome measure
Continued abstinence at 12 months confirmed through CO. Secondary outcome measures: Self-reported continued abstinence at 12 months; point abstinence at 12 months confirmed by CO-oximetry (CO) and self-reported point abstinence at 12 months.
Other variables
At baseline, the following information was obtained: (a) socio-demographic: age, sex, occupation and educational level; (b) lifestyle-related: use of alcohol and other drugs, practice of regular physical activity, fruit and vegetable intake; (c) health-related: history of arterial hypertension, diabetes, hyperlipidemia, obesity, asthma, COPD, ischemic heart disease, stroke, peripheral blood vessel disease, cancer and mental illness (type and use of psychotropic agents); (d) tobacco-related: main reason for wanting to quit smoking, number of cigarettes smoked daily, age at which smoking began, level of dependency as per Fagerström's test, smoking among individuals closest to the patient, number of past attempts to quit smoking, number of days of abstinence, strategy followed during past attempts (with or without professional help and with or without drugs) and reasons for relapse (weight gain, anxiety, insomnia, "smoking does no harm," etc.): (e) intervention-related: preferences in connection with the type of intervention they would have chosen had they been able to choose (individual, group, or either), and the strength of the patient's belief that he/she could quit smoking (on a scale from 0 to 10). During the intervention, the following information was obtained at each visit: the person in charge of conducting it (physician, nurse or both), its length, the number of cigarettes smoked, CO results, whether the participant was taking anti-smoking drugs (nicotine derivatives or bupropion) or not, and the strength of the patient's belief that he/she could quit smoking. Participants were classified as being on nicotine derivatives or bupropion if they were on these drugs during any of the intervention visits. At each follow-up visit, the number of cigarettes smoked and CO values were obtained.
Statistical analysis
We used the chi squared test and the Anova and Kruskal-Wallis tests to ascertain whether randomization had resulted in three comparable groups at baseline, and to make comparisons across the three interventions. We used the Kolmogoroff-Smirnoff test to check the continuous variables for normal distribution.
For the main objective, the analysis was based on intention to treat. Cases lost during the interventions or lost to follow-up were treated as if they were still smokers at 12 months. The study statistician was blinded to the intervention allocation of the participants. Another member of the research team repeated the analysis to assess whether blinding was successful. Continued and point abstinence rates, confirmed by CO and self-report, were estimated. Relative risks were calculated for each outcome measure, along with the reduction in absolute risk and the number of individuals needed to treat (NNT) to obtain a single case of smoking cessation. All these measures are presented, along with their 95% confidence intervals.
To pursue the secondary objective, a bivariate analysis was performed to determine what variables were associated with smoking cessation. The chi squared test for qualitative variables and the Anova and Kruskal-Wallis tests for quantitative variables were used. Multivariate logistic regression was performed to determine if any variables other than group allocation were also associated with smoking cessation. Variables that yielded a significance level of < 0.25 in the bivariate analysis were selected by means of a backward LR. We evaluated at each step the potential confounding effect of the variables eliminated along the way. Multivariate analysis was repeated with forced entry of anti-smoking drugs into the model, and no changes in the final model beta coefficients were observed.
Statistical software SPSS 11.5 for Windows was used.
The study was performed with the approval of the Balearic Islands Ethics Committee.