A useful evaluation design, and effects of the Olweus Bullying Prevention Program
The article presents the logic and other characteristics of an “extended selection cohorts” quasi-experimental design. Possible threats to the validity of conclusions based on this kind of design are discussed. It is concluded that chances are good that conclusions about the effects or non-effects of school-based intervention programs will be roughly correct in most cases. The design may be particularly useful in studies where it is not possible or desirable to use a random selection of “control schools” and it should be of value to both practitioners and researchers. The design is illustrated with a study in which three consecutive cohorts of students ( n approximately 21000) were administered the Bully/Victim Questionnaire before and after some 8 months of intervention with the Olweus Bullying Prevention Program (OBPP). Results indicated quite substantial reductions (by 32–49%) in bully/victim problems. The “time-series” nature of the data showed convincingly that a “history interpretation” of the findings (Cook & Campbell, Quasi-experimentation . Chicago: Rand McNally, 1979) is very unlikely. The data in this project were obtained in the context of a government-funded new national initiative against bullying in Norway. The characteristics of this initiative and the model used in implementing the program in more than 450 schools were briefly described.