This is a randomised experimental study to assess two actions: advice versus MI ().
The two categories of interventions, as well as all initial and follow-up data collection and measures, were conducted by five family physicians working within the Spanish Public Health Care System in two different Health Centres in the city of Albacete. Both Centres attend to an urban population of approximately 48 000 persons each, 13% of whom are older than 65 years of age. The five doctors are members of the permanent staff in their respective centres, each one assigned to attend a roster of 1900 patients over the age of 14 years.
The five GPs had been given specific training in MI techniques by means of role-playing and video recordings, in order to establish and combine the basic contents, both of the brief individual action (anti-smoking advice) and the MI action.
All subjects in this study were patients on the rosters of the five physician–investigators described above. 200 active smoker patients between the ages of 15 and 75 years were recruited during regular visits to their respective GPs, for whatever reason. None of the subjects had been recipients of pre-selection cards nor publicity regarding the trial, nor were they chosen for the study with respect to any particular pathology.
A smoker was considered to be any person who replied ‘yes’ to the question: Do you smoke?
Patients were recruited over a period of 23 months; informed consent was requested from all those taking part in the trial. Exclusion criteria were existence of severe psychiatric disorder, a terminal illness or drug-addiction, or age <15 or >75 years.
The smokers participating in the study were assessed over a total period of 1 year, and follow-ups of the effectiveness of the interventions were conducted after 6 and 12 months post intervention.
Sample size calculation
Calculation of the sample size was made by considering an effectiveness in giving up smoking of 5% with anti-smoking advice and of 20% with MI, that is to say a relative effectiveness four times higher for MI over advice. Two groups of 100 subjects were necessary (α risk level of 0.05% and 90% capacity to detect the difference existing between groups).
Randomisation sequence generation
The patients were randomly assigned to either one of the actions groups by means of a non-block table of random numbers. The assignment sequence established resulted in one group of 86 patients receiving brief advice and another of 114 subjects assigned to MI.
Two hundred non-transparent sealed envelopes containing the interventions (either brief advice or MI) were prepared. Before the start of daily consultations, the GPs conducting the interventions would extract one of the envelopes, not knowing the type of action it contained. The first smoker patient who attended the consultation would be offered the possibility of taking part in the study. If they accepted and signed the informed consent form, the envelope would be opened, upon which the GP would learn of the patient's group assignment.
After opening the envelope, patients in both groups were given verbal and written information about the study's purpose, aims and procedures.
The personal details of each patient were then collected (age, sex, educational level, employment), variables relating to tobacco consumption (presence of disease related to tobacco consumption — chronic obstructive pulmonary disease (COPD) and ischaemic heart disease — number of cigarettes smoked a day, age when the patient started smoking, years smoking) and stage of change, according to the five stages of change described by Prochaska-DiClemente:11
precontemplative, contemplative, action, maintenance and relapse.
The degree of nicotine dependency was assessed by Fagerström's test.13
Depending on the result that each smoker gives to each question, a certain mark is obtained, that may vary from 0–10 points.
A degree of slight dependency is considered when the test varies from 0 to 3 points; moderate dependency is from 4 to 6 points; a severe degree of dependency is 7 points or over.
In all patients, the level of carbon monoxide in the air expired at the start of the study was measured by means of a micro smokerlyser carbon monoxide (CO) monitor14
(Bedfont Technical Instruments Ltd). CO values were used as abstinence markers, 6 and 12 months after the action. Figures of ≥10 ppm of CO indicate smokers; 6–10 ppm sporadic smokers, and <6 ppm, non-smokers.15
In the same first consultation, following data collection and CO measurements, the action assigned to each subject case was carried out.
Patients receiving anti-smoking advice were given one intervention session consisting of a personal talk by their physician, lasting approximately 3 minutes. The dangers of smoking were explained, as well as the advantages of giving it up. The information given in all advice consultations was the same and in accordance with the recommendations of the Smoking Department of the Spanish Pneumology and Chest Surgery Association (SEPAR).16
Patients assigned to MI were given the first of a total of three 20–minute interviews conducted in the physician's office. There was no established protocol for time lapse between interviews; rather, appointments for the subsequent session were set up with the GP at the patient's convenience.
Patients in both intervention groups showing high nicotine-dependency (Fagerström's test scores of ≥7), were offered the possibility of concurrent treatment with bupropion, the first non-nicotine medication approved for treating tobacco dependence.17
All patients were contacted at 6 and 12 months post intervention for follow-up appointments. Smoking habits were assessed 6 and 12 months post intervention, by measuring number of cigarettes smoked a day, the degree of nicotine dependency according to Fagerström's test, stage of change, as well as level of CO in expired air in all those taking part in the MI group and in those in the advice group who reported abstinence.
The final primary variable measured was success index, namely point prevalence of abstinence at 6 and 12 months post intervention. Abstinence was subjectively ascertained by means of direct personal testimony, and objectively confirmed by obtaining values of less than 6 ppm of CO in expired air (reference value acknowledged as a cut-off point between smokers and non-smokers). Failure of abstinence was defined as continuation of the smoking habit or non-attendance of follow-ups to confirm abstinence.
Statistical analysis was made in blind form, without knowing the identification labels of the groups that were compared. The results were analysed using SPSS. First of all, a description was made of the variables studied in both groups, comparing the distribution of the determining factors that may have affected the final result, and then a comparison was made of the proportion of successes by means of the χ2 test.
In order to evaluate the modifying variables of the effect and avoid confusion factors, recourse was made to multivariant analysis, constructing a logistic regression model by the step-by-step inclusion method, in which the dependent variable was the success or failure of the anti-smoking action, after both 6 and 12 months.
The trial was analysed by intention to treat, evaluating each subject in the study group to which they were randomly assigned. The extent of the therapeutic effect and the accuracy in its estimation was considered, calculating the reduction in relative risk, the reduction in absolute risk and the absolute increase in benefit, as well as the number of patients it would be necessary to treat in order to avoid a negative result.
The study was approved by the medical research ethics committee of the Albacete University Hospital Complex (Spain) on 3 April 2003.