ABSTRACT
This paper shows the evaluation of the effectiveness of a selective prevention on drug use in adolescents, based on the Theory of Planned Behavior by Azjen. To develop this program, different theoretical models were evaluated considering their suitability to the institutional context in which it will be implemented. The criteria used to select a model that could be useful as a basis to design and evaluate a preventive intervention for drug use included: a) incorporation of protective and risk factors that could be malleable; b) consistency, parsimony and theoretical economy; c) a demonstrated explanatory and predictive capacity; d) empirical effectiveness; e) practical applicability. One of the models that complies with these requirements is the Model of Planned Behavior by Azjen, which proposes that the most immediate causes for drug use are the intentions of the subject to consume them or not. These intentions are determinated by the «attitudes¼ toward drug use, by the normative beliefs or «subjective norm¼ and by the Perceived Behavior Control. Attitudes toward the behavior are a person's overall evaluation of the behavior (i.e drug use) and the corresponding positive or negative judgments about it. The normative beliefs or subjective norms are a person's own estimate of social pressure to use or not to use drugs. Subjective norms have two interacting components: beliefs about how other people, who may be significant to the person, would like them to behave (normative beliefs), and the positive or negative judgments about each belief (outcome evaluations). Perceived behavioral control is the magnitude to which a person feels able to carry out the behavior. It includes two aspects: how much control a person has over the behavior; and how confident a person feels about being able to perform or not the behavior. It is determined by control beliefs about the power of both situational and internal factors to inhibit or facilitate the performance of the behavior. Perceived behavioral control, the last element introduced in the theory, along with the attitude to conduct, and the subjective norm, contribute, all of them, to predict the behavior intention. Generally speaking, there is important empirical evidence concerning the predictive and explicative capacity of this model in different populations. Once the theoretical model was chosen, indicators related to constructs of the Theory of Planned Behavior were elaborated adapting these constructs to the features of middle education Mexican population by means of a series of interviews with focal groups. Based on these indicators, a scale was constructed to prove the explanatory capacity of the theoretical model in Mexican population. The reliability and validity of this self-applied questionnaire was proved. Once this was done, based on these antecedents, the model was adapted in a practical sense. This means that the content, objectives and techniques for a preventive intervention were developed. This preventive intervention was piloted and then evaluated through the aforementioned scale. The program included attitudinal and normative components, conformed by informative strategies and persuasive messages directed to an attitudinal change, as well as the development of strategies of behavioral control focused on social abilities that included components derived from social learning theory, and a series of cognitive behavioral techniques accorded to the Planned Behavioral Theory. It was expected a reduction in the drugs use intention by means of a change of drug use favorable beliefs as well as reinforcing unfavorable beliefs of drug use. It was also tried to change the perception about the magnitude of drug users in the subject's immediate surroundings and on its perception about social acceptance or tolerance for drugs. Also it was tried to increase the perception of self control, in order to the develop behavioral control skills to refuse the offer of drugs. The first sessions (devoted to work on subjective norm) were directed to create an interest in the participants regarding to their relation with favorable situations to drug consumption, and to modify their perception about the real magnitude of drug use and about approval and social tolerance to them, both topics frequently overestimated for some adolescents. These sessions were also devoted to identifying beliefs associated with drug use and the value that participants give to these beliefs, in order to question those that are established upon false premises. The next sessions (devoted to perceived behavioral control) had as an objective to learn appropriated behavioral responses to confront risk situations, in order to increase the perception of self-control in those circumstances. This was achieved by means of modeling, essay and reinforcing techniques. This model was designed to be applied in groups no greater than 15 persons, twice a week in five sessions of 50 minutes each. The program was applied by professional personnel such as psychologists or social workers with previous experience in drugs use prevention. The program was implemented in three groups (one for each grade) of five high schools in Mexico City and was applied to three groups of school, randomly chosen; other three groups, in the same grades, were used as control groups. The groups were randomly chosen. Other three groups, in the same grades, were used as comparison groups. Then, the final sample was composed by 250 participants (96 from intervened groups and 154 from comparison groups) from 1 2 to 15 years old, and with slightly more men than women, but equivalent for cases and control. The results showed that the intervened group had a statistical significant reduction in the intention of drugs use. On the contrary, the comparative group showed an increasing intention to use them. With respect to the set of variables that predicted the behavioral intention, the perceived behavioral control stands out as the variable that had the greatest change. There were no significant differences in pre-post measures in the control group. Differences between pre-post measurements were also contrasted between both groups using a Student's /test that showed significant differences in perceived behavioral control and behavioral intention variables. Finally, in order to get a greater control on the test scores, an ANCOVA analysis was applied using the post-test scores as dependent variable and the pre-test scores as covariables. This analysis was useful to corroborate the significance of the drug use intention in the future, mainly in situations that require an amount of self-control, while attitude and normative variables did not show significative changes. Outcomes confirmed the pertinence to give greater resources (time, quantity, and complexity of activities, didactic materials, etc.) to the sessions devoted to developing behavioral control skills. These results can be considered satisfactory, because the main objective of the program was to reduce the intention to use drugs; however, it is also necessary to strengthen the attitudinal and normative components. It is necessary to consider that the variable «subjective norm¼ obtained the lowest levels in confidence, possibly because of the use of self-reported answers in a variable so sensitive to the influence of social elements. For this reason, it is necessary to develop questions that diminish this element that, according to Doll and Azjen, can explain, even a 5% of variance in «behavioral intention¼. Finally, it must be considered that this evaluation shows the effectiveness of the program to achieve the expected changes in behavioral intention variable only in controlled situations. It is necessary to investigate if it is possible to obtain similar results in more usual conditions and with other populations. This means that as well as to grant the internal validity of the evaluation it is also necessary to establish its external validity.
Se presentan los resultados de la evaluación de la eficacia de un programa de prevención selectiva del consumo de drogas para adolescentes, basado en la teoría de la conducta planificada de Ajzen. Para el desarrollo de este programa se identificaron y evaluaron distintos modelos teóricos. Los criterios considerados para seleccionar un modelo que pudiera servir de base para el diseño y evaluación de una alternativa de intervención preventiva del uso de drogas, teórica y empíricamente sustentada, comprendieron: a) la inclusión de factores de riesgo o protectores maleables; b) consistencia, parsimonia y economía teóricas; c) probada capacidad explicativa y predictiva; d) eficacia empírica; e) aplicabilidad práctica. Uno de los modelos teóricos que cumplen satisfactoriamente estos requisitos es el Modelo de la Conducta Planificada de Ajzen, el cual plantea que la causa más inmediata del uso de drogas son las intenciones del individuo respecto a consumirlas o no. Estas intenciones están determinadas a su vez por dos componentes; por una parte, las actitudes hacia el consumo, y por otra, las creencias normativas o norma subjetiva. Las actitudes están conformadas por el conjunto de creencias sobre las consecuencias del consumo y por el valor afectivo que tales consecuencias tienen para el sujeto. Las creencias normativas o norma subjetiva también están determinadas por dos componentes. Por un lado, la percepción de que otras personas significativas para el sujeto aprueban o desaprueban el consumo y, por otro, la motivación del sujeto para acomodarse a las expectativas o deseos de estas personas. El control conductual percibido, último componente introducido en la teoría, contribuye ¡unto con la actitud hada la conducta y la norma subjetiva a predecir la intención conductual. En general, se cuenta con importante evidencia empírica acerca de la validez predictiva y explicativa de este modelo, en relación con el consumo de drogas entre distintas poblaciones. Una vez elegido el modelo teórico se elaboró una escala de medición para probar su capacidad explicativa para el caso de uso de drogas en población mexicana. Probada la capacidad explicativa del modelo, se llevó a cabo su adaptación práctica, en términos de desarrollar contenidos, objetivos y técnicas de una intervención preventiva basada en el mismo. Por último, se realizó la prueba piloto y la evaluación de la aplicación controlada de tal intervención. La evaluación de resultados se apoyó en un diseño experimental con prueba-postprueba y un grupo control. El programa se aplicó en cinco escuelas secundarias de la Ciudad de México. Se intervino a tres grupos de cada escuela, uno por grado, elegidos aleatoriamente. La muestra final, una vez depurada, quedó conformada por 250 jóvenes (96 casos y 154 controles) de entre 12 y 15 años de edad. Para la evaluación se utilizó una cédula creada ex profeso y probada previamente en una muestra de 1 200 alumnos, mostrando buenos niveles de confiabilidad y validez. Los resultados muestran que en el grupo intervenido tuvo lugar una disminución estadísticamente significativa de la intención de usar drogas, en tanto que los alumnos del grupo comparativo mostraron, por el contrario, un incremento en la intención de uso durante el mismo lapso. Del mismo modo, entre las variables antecedentes de la intención conductual, a saber, actitud, norma subjetiva^ control conductual percibido, la variable que mostró un mayor cambio fue esta última. También se contrastaron las «puntuaciones de ganancia¼ (diferencias antes-después) del grupo de los casos contra las del grupo de los controles, con lo que se pudo observar que las diferencias significativas entre ambos grupos se presentaron en las variables control conductual percibido e intención conductual. Finalmente, mediante el Modelo Lineal General (MLG) ANCOVA, se pudo corroborar la significativa reducción de la intención de utilizar sustancias y el incremento en la percepción de autocontrol, mientras que la actitud y la variable normativa no mostraron cambios significativos, lo que confirma la pertinencia de haber dotado de mayores recursos (tiempo, número y complejidad de las actividades, materiales didácticos, etc.) a las sesiones dedicadas al desarrollo de habilidades de control conductual, sobre la base previamente probada, tanto en población anglosajona como entre jóvenes mexicanos, de que esta variable suele tener un mayor peso en la explicación de la intención de usar drogas.
ABSTRACT
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Summary The need of cost-effective drug abuse prevention programs has derived in a growing interest to develop scientific based alternatives. On this context, this study forms part of a project for the design and evaluation of a theoretical and empirically sustained intervention for illicit drug abuse prevention among Mexican junior high school students. Starting with the revision and assessment of different theoretical models that could be adapted to the conditions of the institutional context wherein the intervention will be developed, the Azjen and Fishbein's Theory of Planned Behavior was chosen. This theory includes proximal cognitive and attitude factors directly related to the initiation of drug use. In accordance with it, the experimental use of substances is a result of the intention of consuming them, which, in turn, depends on three elements: a) the attitude toward the drug use, b) the normative beliefs on this matter (subjective norm) and c) the perceived behavioral control regarding drug use or, in turn, confronting social pressure. In a first instance, several items were developed adapting the constructs of the Theory of Planned Behavior to the target population's characteristics. On this base, the reliability and validity of a self-applied questionnaire for the measurement of the variables of the model was proved. In this work are reported the findings of the evaluation of Theory of Planned Behavior's potential to predict both behavioral intention of using illicit drugs and consumption of substances among Mexican high school students, in order to set a precedent to apply the model later on in the design and evaluation of a preventive intervention directed to such population. Method: The study was carried on with an ex post facto, correlational design, and with a non-probabilistic sample of 1,019 subjects. Sample. The sample size was estimated considering the possibility of selecting a subsample of drug users and comparison subjects for a post-stratified analysis, assuring a statistical power of 80% and adequate sensibility and stability. Therefore, this work includes the performed analyses with a sample of 75 drug users and 75 non users, paired by gender, age, school grade and occupation. Instrument. The instrument was a self-applied questionnaire specially developed for the study, according to information obtained in previous focal groups interviews with high school students. The questionnaire showed a global realiability of 0.9154 and between 0.62 and 0.94 in each one of its scales, which included: behavioral beliefs (0.9121), attributed value to behavioral beliefs (0.7964), normative beliefs (0.6480), subject's disposition to adjust to normative expectations (0.8564), descriptive norm (0.6254), drug use opportunities (0.8129) and perceived behavioral control coping with such opportunity situations (0.9442). A factorial analysis of principal components yielded 16 factors of at least three items each, with factorial weights higher than 0.4, and closely attached to Theory of Planned Behavior's variables, with an explained variance of 59%. Analysis. Previous to data analysis, normality tests (Kolmogorov- Smirnov) were performed, indicating the necessity to apply nonparametric tests of differences and to transform the data to be adapted to the requirements of later parametric analyses. A correlation analysis was carried out to prove the association between behavioral intention and drug use, as well as between the different components of the Theory of Planned Behavior. Finally, linear and logistic regression analyses were conducted to determine the explicative potential of the model and the predictive weight of each variable on the model with regard to the behavioral intention and the consumption of drugs. Findings: According to the Mann-Whitney test, compared with students who had not used drugs, subjects that used them at least once in their life showed more favorable attitudes toward consumption (median= 6.9 vs. 3.9, z=-5.22, p=0.000), perceived more social tolerance (median=3.8 vs. 3.5, z=-2.27, p=0.023), were more willing to give in to social pressure for using substances (median=2.0 vs. 1.0, z=-5.598, p=0.000), perceived a higher number of users among their significant others, and less negative consequences Salud Mental, Vol. 30, No. 1, enero-febrero 2007 69 of drug use in themselves (median=16.3 vs. 7.1, z=-4.246, p=0.000), and felt less capable of behavioral control when coping with opportunities for consumption, which, in turn, are more frequent in their case (median=5.7 vs 1.8, z=-6.76, p=0.000). The correlation between the intention and the behavior of drug use (r=0.41, p<0.000) was allocated inside the range reported in other populations. Drug use intention correlated with attitude toward drug use at r=0.45 (p=0.000), with subjective norm, including additional components at r=0.48 (p=0.000), and with perceived behavioral control at r=0.59 (p=0.000). Drug use correlated with attitude at r=0.51 (p=0.000), with subjective norm at r=0.28 (p=0.001), and with perceived behavioral control at r=0.37 (p=0.000). Linear regression analysis yielded that the model explained 34% of the variance of drug use intention, which increased to 38% when adding personal and descriptive norm elements to the subjective norm construct. Behavioral control (measured on the basis of the product of exposition to drug use facilitating situations punctuations by perceived behavioral control to cope with these situations punctuations) was identified as the best predictor of drug use intention (B=0.32, p=0.001), followed by attitude toward drug use (B=0.24, p=0.004) and subjective norm, which originally showed a non-significant effect but increased its predictive weight when additional elements were added (B=0.24, p=0.004). According to the logistic regression analysis, behavioral control is also the best predictor of illicit drug use on the model (odds ratio= 1.42, p<0.000). On the contrary, subjective norm (including personal and descriptive norm) and attitude (odds ratio=1.144, p=0.06) were not significant predictors of drug use. Discussion: In general, this findings indicate that the Theory of Planned Behavior showed an acceptable predictive capacity (similar to that found in other populations), and can be taken as a valid theoretical ground to develop a preventive intervention directed to Mexican students of high school education. As is the case with other populations, the variable in the Planned Behavior Theory with more predictive weight was perceived behavioral control, followed by attitude to drug use and, in third place, by subjective norm. Despite it could be supposed that subjective norm would have a higher predictive weight in Mexican teenagers, findings probably reflected idiocentric and individualistic tendencies reported in other studies. Results also point out to the convenience of including it in the program of intervention informative components to produce an awareness effect and an impact in the intention of using drugs. Still, they indicate above all, the need to integrate components directed to the development and reinforcement of behavioral control abilities that have an effect in the use of drugs itself. Specifically, it is considered the convenience of including components for the development of group pressure resistance abilities and assertive communication, appropriate to the contexts in which young people face drug abuse risk situations.