Indicators must serve a clear purpose, i.e. measuring to what extent a policy has been properly implemented and its objectives achieved. Another important factor in choosing your indicators is the ease with which data can be collected; collecting data should not be more costly than the value of the information they provide.
According to the Commission's evaluation rules all its activities have to be evaluated on a regular basis. For spending proposals evaluation is compulsory, and many other policy initiatives also contain a review clause, that will require evaluation of such policies since they have been put in place. Evaluations should be announced and described in advance, with a clear indication of the timing, the main focus and purpose, who will be responsible for carrying them out, and to whom the results will be addressed.