The relevance model is one in which the key criterion against which the intervention is evaluated is whether the underlying policy problem has been solved completely, partly or not at all. Firstly the policy intervention must be ‘relevant’ i.e. “adequate, useful, sufficient and proper” for addressing the policy problem. Based on scientific evidence and expert opinion the ‘relevance’ of the policy intervention to the policy problem can be assessed even before the intervention is implemented. Once the intervention is implemented, any subsequent changes in the problem situation can be evaluated.