| Criterion |
Explanation |
| Strong Association |
There must be correlation between the variables: A strong association should not only exist between the intervention and outcome, but also between the proposed mechanism and the intervention, and between the proposed mechanism and treatment outcome. |
| Specificity |
Change in the intervention is uniquely related to change in the proposed mechanism, and change in the proposed mechanism is uniquely related to change in treatment outcome. |
| Gradient |
Amount of change in the intervention is directly related to the amount of change in the proposed mechanism, which consequently influences the degree of patient change. Greater activation of the proposed mechanism which corresponds with greater change in outcome supports the operation of a change mechanism or mediator. |
| Temporal Relation |
A change in the proposed mechanism precedes a change in outcome. This requires simultaneous and repeated assessment of the proposed mechanism and outcome throughout the course of the intervention. |
| Consistency |
Findings are replicated across studies, samples, and conditions. However, inconsistency in findings may point towards a moderating variable rather than evidence that the proposed mechanism of change does not exist. |
| Experimental Design |
Allows careful manipulation of variables to demonstrate a causal effect of treatment upon outcome, and of the proposed mechanism of change upon outcome. Manipulating the proposed mechanism and observing a differential effect on outcome supports the case for a mechanism of change. |
| Plausibility and Coherence |
There needs to be a plausible explanation of the process through which the mechanism of change has an effect, and this explanation should be coherent with existing knowledge. |
| In concert |
The satisfaction of these criteria ‘in concert’ strengthens the case for a mechanism of change, and this is unlikely to be achieved in one study alone. At a minimum, the criteria of strong association, temporal relation, experimental design, and specificity are required to support the operation of a mechanism of change. |
