The Practice of Evidence in Evidence-based Practice: A Conceptual History of Evidence in Psychological Clinical Practice

The concept of ‘evidence’ plays an important role in the epistemology of science, a role that has been amplified recently within psychology with the advent of the evidence-based practice (EBP) movement. However, psychologists have devoted little attention to exploring the meaning of the concept of ‘evidence.’ The purpose of this project was to examine the concept of ‘evidence’ in social contexts throughout history, in psychology, and finally in the EBP movement in clinical psychology, with the aim of elucidating: (1) definitions and contexts of employment of ‘evidence’ throughout the history of Western thought, (2) definitions and the role of evidence in psychology and EBP, (3) philosophical and conceptual issues related to various conceptualizations of ‘evidence’ and the implications of these for psychological practice and research. Historical, archival, and qualitative methods employed towards this end included: (1) a review of historical literature and sources on ‘evidence,’ (2) interviews with members of the APA Task Force on EBP, (3) a review of relevant archival records of Task Force deliberations, (4) a qualitative analysis of published articles that relate to the EBP movement, and (5) a review of philosophical treatments of evidence and conceptual issues that arise in the EBP literature. The historical review revealed that conceptualizations of ‘evidence’ and its role in the generation of knowledge have shifted throughout human history and across social contexts. Shifts in conceptualizations of evidence within the narrower context of science have been accompanied by changes in scientific practices and conventions. A review of the evidence-based practice literature in psychology revealed a multitude of conceptualizations of ‘evidence’ and its role within the EBP literature. The review of philosophical treatments of ‘evidence’ helped to highlight different implications of conceptualizations of ‘evidence’ for scientific practice. For instance, the assumptions inherent in conceptualizing evidence in various ways are at times conceptually, logically, and practically incompatible. The definitional plurality of evidence in the EBP discourse is problematic for coherent scientific and clinical practice in psychology. By drawing attention to such matters, this thesis encourages clinical psychologists to attend more carefully to EBP initiatives and the implications these carry for clinical practice.