Impact evaluation measures how successful the program/project/policy was at achieving its objective. In this case, emphasis falls on the accomplishments of the program and a comparison to the declared program goal. Impact evaluation is the most wide-spread approach and is used by international non-governmental organizations, as well as by governmental institutions and private companies.
Impact evaluation is even more informative when baseline research is available. A comparative analysis of the baseline research and impact evaluation will give a very precise picture of the efficiency of the program.