MEASURING THE INTERVENTION IN EFFECTIVENESS RESEARCH

Inconsistent implementation of the intervention in the field setting p resents a threat to the validity of the conclusions of an effectivenes s study. Inconsisient implementation results in variability in the act ual dosage of the intervention received by the participants, which lea ds to variability in outcomes achievement and, consequently, to Type I I error. This article discusses the methodological implications of inc onsistent intervention implementation and advances a strategy as a sol ution to this problem. The strategy proposes to quantify the dosage of the intervention as a continuous variable and to use this variable in the statistical analysis. The benefits of this strategy are illustrat ed with an empirical example from the Self-Help Intervention Project.