Program evaluations are systematic studies that use research methods to address specific questions about program performance. Evaluation is closely related to performance measurement and reporting. Whereas performance measurement entails the ongoing monitoring and reporting of program progress toward preestablished goals, program evaluation typically assesses the achievement of a program's objectives and other aspects of performance in the context in which the program operates. In particular, evaluations can be designed to isolate the causal impacts of programs from other external economic or environmental conditions in order to assess a program's effectiveness. Thus, an evaluation study can provide a valuable supplement to ongoing performance reporting by measuring results that are too difficult or expensive to assess annually, explaining the reasons why performance goals were not met, or assessing whether one approach is more effective than another.