Date of Award


Publication Type

Doctoral Thesis

Degree Name





Psychology, Computerized intervention, Contingency management, Motivational intervention, Smoking cessation


Sherry Stewart




Approximately 20% of Canadian adults currently smoke, despite widespread knowledge of the significant health problems associated with tobacco use. Of the many smoking cessation interventions developed, contingency management (CM) appears to be among the most efficacious. This type of external motivation has previously been shown to be very efficacious when the contingency is in place, but its effects tend to diminish once the contingency is removed. In contrast, motivational interviewing (MI) is designed to increase an individual's internal motivation for behaviour change. Studies have shown this type of intervention to produce modest effects for smoking cessation, although follow-up data suggest that the effects of such interventions can be relatively long-lasting.

This study evaluated the combined efficacy of CM and a brief computer-delivered motivational intervention (CDMI) for smoking cessation. This CDMI is based on the principles of MI but is modified from this traditional approach in order to accommodate a computerized delivery of the intervention. The intention was to harness the short-term effectiveness of CM while enhancing or perhaps extending its effects by combining it with CDMI. Using a sample of 48 opiate-dependent persons receiving methadone maintenance therapy, this randomized trial compared rates of smoking cessation for patients receiving CDMI and CM together to those of patients receiving CDMI alone or treatment as usual.

Results indicated that the combination of CDMI and CM was most effective at producing reductions in breath carbon monoxide during the four-week study period, while CDMI only participants endorsed the highest levels of motivation to quit smoking. At five-week follow-up, CDMI only participants continued to show reductions in number of cigarettes smoked, while CDMI plus CM participants increased their use of cigarettes relative to when the intervention was in place. These results are discussed with respect to the Self-Determination Theory and are used to suggest directions for future research and larger scale studies.