In this chapter, you gained an understanding of psychotherapy and its evolution. You observed its transformation from an intuitive treatment approach to an evidence-based intervention grounded in scientific findings. Additionally, you explored the concept of common factors and their influence on the development of outcome research within the field.

You learned that the history of psychotherapy research can be structured by the idea of “four phases”.

Phase I (1920 – 1954) involved anecdotal and uncontrolled case studies, which faced growing criticism due to their statistical limitations. Hans Eysenck, a prominent critic, provocatively contended that psychotherapy lacked efficacy. Eysenck’s critiques spurred the adoption of statistical methods in psychotherapy research.

Phase II (1955 – 1969) witnessed substantial growth in psychotherapy research, aiming to establish it as a scientific discipline. The 1960s brought new challenges as Eysenck launched another critique. Phase II research focused on countering his claims, highlighted by advancements like pre-post-follow-up designs and investigating non-linear relationships.

Phase III (1970 – 1983) refined and expanded methodologies. Highlights included initial meta-analyses, adopting randomized controlled trials from pharmacology, and investigating potential negative effects. The significant accomplishment of Phase III was conclusively addressing Eysenck’s criticism: Psychotherapy is effective.

Phase IV (1984 – Today) shifted from verification to discovery in research, evident in the rise of qualitative and mixed-methods approaches. Researchers also grappled with efficacy versus effectiveness questions. The Internet’s emergence offered both unique opportunities and challenges.

Saul Rosenzweig introduced the idea of a set of common factors that were integral parts of all forms of therapies, thus also suggesting that treatment outcomes were not driven by therapy-specific elements. Rosenzweig illustrated this idea by referring to the dodo bird analogy from Lewis Carroll’s Alice in Wonderland: “everybody has won, and all must have prizes.”

To help you memorize important events, you can download and fill out this timeline.