Causal identification in design networks

When planning and designing a policy intervention and evaluation, the policy maker will have to define a strategy which will define the (conditional independence) structure of the available data. Here, Dawid's extended influence diagrams are augmented by including 'experimental design' decisions nodes within the set of intervention strategies to provide semantics to discuss how a 'design' decision strategy (such as randomisation) might assist the systematic identification of intervention causal effects. By introducing design decision nodes into the framework, the experimental design underlying the data available is made explicit. We show how influence diagrams might be used to discuss the efficacy of different designs and conditions under which one can identify 'causal' effects of a future policy intervention. The approach of this paper lies primarily within probabilistic decision theory.