12.1 The need for policy evaluation
If we lived in a world of complete certainty and perfect administration there would be no need for evaluation: having selected the best option and put it into operation we would know in advance what its effects would be. However, we rarely have such certainty. Our understanding of many issues, especially social problems, is imperfect or even contested (see chapter 7 on issue definition). Our understanding of how government intervention will work and what its effect will be is therefore also limited. Further, this government intervention is only one of many influences on the target problem, because unforeseen changes may arise, because this programme may interact with a number of other programmes, and because it may be difficult to separate out the effects of a 'new' programme from the long-term effects of programmes which it replaces. All these problems make it both necessary to monitor the delivery of a programme and evaluate its success, and very difficult to do so.
Although evaluation is concerned with what happens once a policy has been put into effect, it is important that we should not leave it until that stage before we consider how we might go about evaluating the policy. If we do so, we may find that evaluation is impracticable or produces inconclusive results. The time to consider evaluation is at the options selection and programme design stages. The type of information required can be specified in advance. More dramatically, the extent to which an option is capable of being evaluated can be made one of the criteria for selection. Finally, the policy analysis