The extent to which one program, project, or instructional material produces equal or better results than competitors that cost about the same amount of time, effort, and resources; or the extent to which an object produces the same results as competitors but is less costly.
Yarbrough, D. B., Shulha, L. M., Hopson, R. K., and Caruthers, F. A. (2011). The program evaluation standards: A guide for evaluators and evaluation users (3rd ed.). Thousand Oaks, CA: Sage.