Key points

•  Evaluations can be designed to answer a broad range of questions on topics such as how the policy was delivered, what difference it made, whether it could be improved and whether the benefits justified the costs.

•  Broadly, these questions can be answered by three main types of evaluation. Process evaluations assess whether a policy is being implemented as intended and what, in practice, is felt to be working more or less well, and why. Impact evaluations attempt to provide an objective test of what changes have occurred, and the extent to which these can be attributed to the policy. Economic evaluations, in simple terms, compare the benefits of the policy with its costs.

•  Understanding why an intervention operated in a certain way and had the effect it had generally involves combining the information and analytical approaches of the different types of evaluation and they should, therefore, be designed and planned at the same time.

•  The choice of evaluation approach should be based on a statement of the policy's underlying theory or logic and stated objectives - how the policy was supposed to have its effect on its various target outcomes. The more complex the underlying logic, the more important it will be to account for other factors which might affect the outcome.

•  Having a clear idea about the questions that need to be addressed and the required type(s) of evaluation at an early stage will help inform the design of the evaluation and the expertise required.