As indicated, there is no single agreed concept of “evidence” Thomas (2004: 1). It is emphasized that evidence takes different forms and is valued differently in different contexts, such as the legal system, natural
science, medicine and the humanities. The evaluation community, like any other scientifi c community, operates with a set of beliefs about what counts as knowledge, what the role of “theories” is, how to collect data, how to weigh different forms of evidence, and how to construct logical and compelling arguments. This shared set of assumptions and beliefs allows evaluators to engage in peer review, argumentation, criticism, and to systematically build a body of shared knowledge. The crucial institutions that help to build this community are journals, evaluation associations, conferences, academic institutions, and evaluation groups inside larger organiza tions. The processes used are education and training, accreditation, peer review, and critical engagement with each other’s work. In the evaluation community, these institutions and processes have become increasingly global in the last 20 years, and this book is a testimony to that. However, the evaluation community differs in an important respect from other scientifi c communities. The practice of evaluation has for some time been thought of as a meta-discipline (Scriven, 2003; 2005; Coryn and Hattie, 2006) meaning that it draws upon the results of other disciplines in arriving at judgments within its own practice. For example, an evaluation of an intervention to improve the quality of health care will inevitably draw upon the work of health economists, physicians, behavioral psychologists, health sociologists, and patient groups. Therefore, evaluators must concern themselves not only with what they consider to be evidence but also with how other disciplines address this question. This book seeks to examine and explain the intersection between the practice and theory of evaluation and the rise of the evidence movement.