Outcome evaluation is the step that is commonly associated with evaluation: determining whether an intervention was successful. It is also the most desirable part of an intervention, although the most difficult to carry out. First of all, avoid the common mistake made by many project leaders: thinking about defining objectives and outcome indicators too late, when the project has already started or even when it is about to end. The term ‘outcome evaluation’ indicates the type of data that needs to be collected — information on changes in the target group (intermediate or final); in contrast, the term ‘summative evaluation’ is derived from when (at which stage of the intervention) the data are processed (typically after the project has ended). Thus, outcome evaluation is ideally prepared for at the planning stage of an intervention. If a pre–post evaluation design is required, it is often necessary to obtain data on several indicators (at baseline) before the intervention starts... (EUDA Prevention and evaluation resources kit (PERK))

See also, EUDA (2017) Evaluating drug policy: a seven-step guide to support the commissioning and managing of evaluations and EUDA webpage: Drug policy evaluation in Europe — topic overview and EUDA Evaluation Instruments Bank