6.15 The first stage in populating the evaluation framework should be to establish what is already known about the intervention to be evaluated or what can readily be learned about it. This first stage is important for at least four reasons:
• it may be that there is already sufficient evidence on the likely effectiveness of an intervention so that further primary evaluation is unnecessary;
• it is more likely that the existing evidence may be ambiguous, inconclusive, or of uncertain quality indicating that further evaluation is necessary and that specific aspects of the policy intervention in question need addressing;
• any single evaluative study may illuminate only one part of a policy issue, implying that it might be appropriate to focus an evaluation on specific aspects of the evidence base where existing information is lacking; and
• existing findings may be sample, time or context specific. This will make it difficult to establish the generalisability and transferability of findings from the existing research evidence which, in turn, will influence what requires evaluating.