Date of Award


Degree Type


Degree Name

Doctor of Philosophy in Psychology



First Advisor

James O. Prochaska


Despite the extensive evidence of the beneficial aspects of substance abuse treatment, questions on what contributes to successful outcome continue to arise. It is important to research who will be more likely to benefit from which modalities of treatment programs and for what length of treatment. Systematic investigations that include individuals' attitudes, intention and behavior towards their drug use are necessary to better understand the interaction between individual characteristics and treatment factors, as well as their effects on treatment retention and outcome. The Transtheoretical Model of Change offers a promising systematic framework for this purpose (Prochaska & DiClemente, 1983, 1984, 1992).

This study examined the predictive values of two constructs of the Transtheoretical model: stages of change and decisional balance on dropouts and outcome in substance abuse treatment (N=710). Both dynamic and static predictors of treatment dropouts and outcome were investigated. The current investigation is divided into four studies. The Change Assessment for Drug Use (CAD) was developed with sound psychometric properties in Study I. Study II searched for the best stage allocation method in using the CAD and its validation. Findings indicated that cluster analysis was the best stage allocation method. Study III investigated predictors for treatment dropouts and continuers. Dropouts were defined as individuals who dropped out of treatment within the first 60 days of the program. Significant predictors for dropouts included being in precontemplation, lower education, more previous treatment experience and perceiving treatment for social problems as more importance. In Study IV, both predictors at admission and discharge were examined for short-term (3-month post discharge) treatment outcome. Successful outcome was defined as abstinence of drug use since exit of treatment. Being in the preparation stage of change at baseline, having lower depression level at discharge and longer length of stay in treatment were significant predictors for successful outcome. Results indicated that dynamic predictors such as stages of change, length of stay and depression level outweighed all static variables, such as subject characteristics, for prediction of short-term outcome. Implications of current and future directions of research were discussed.



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