Harvard Professor Carol Weiss probably started it all off with her work 'Evaluation Research: Methods of Assessing Program Effectiveness', published in 1972.
Basically, she examined the methodologies used by researchers tasked with examining the effectiveness of particular strategies, irrespective of whether such strategies were applied to education (her specialist field) or to the wider world. That work, and her later volume 'Evaluation: Methods for Studying Programs and Policies' (1998), has spawned a science (or pseudo-science?) of studying the way that those charged with evaluating policies carry out their tasks. There are now societies all over the world dedicated to such research, including here in the UK:
http://www.evaluation.org.uk/about-us/about-ukes
If you
really want to try to make some sense of it all, this might help:
http://www.hfrp.org/evaluation/the-evaluation-exchange/issue-archive/evaluation-methodology/evaluation-theory-or-what-are-evaluation-methods-for