THE COMMON FACTORS THEORY: EXPLORING THE EVIDENCE AND CRITIQUES OF THE COMMON FACTORS THEORY. AN ARGUMENT FOR TECHNICAL ECCLETICISM

For decades the clinical psychology community has been grappling with a key question: what causal mechanisms of changes result in improvements for clients. One theory, known as the Common Factors Theory, posits that therapy is effective through a set of therapeutic factors that are common across all models of psychotherapy. Researchers point to the finding of treatment equivalency consistently indicated by meta-analyses’ in support of this theory. And whilst this theory is conceptually alluring, there are a number of pitfalls that make it unfounded. In this thesis I explored these pitfalls and critiques, namely the conceptually vague nature of common factors, the poor statistical evidence, and how e- therapy challenges the Common Factors Theory. Furthermore, I drew attention to the point that literature does exist which indicates that for some specific problems, presentations or populations literature has indicated that specific techniques or treatments are statistically superior (in line with the specific factors theory). Therefore, this thesis argued that therapy likely works through a combination of common and specific factors, to differing extents for different presentation. Furthermore, it argued that the treatment equivalency findings are both an artefact of poor statistical methods, but more importantly representative of system that is overwhelmed by noise. Our diagnostic categories and models of psychotherapy are too vague for any statistical interpretation or practical use. Therefore, it is important that we shift towards a more fine-grained approach where clinicians are able to identify problems as opposed to disorders and take a technically eclectic approach to responding to and treating identified problems that spans multiple different models of psychotherapy.