How qualitative methods advance the study of causation in psychotherapy research.

Objective: The use of qualitative methods for investigating causation has been controversial ever since the "paradigm wars" of the 1980s. Quantitative and experimental researchers have largely dismissed the relevance of qualitative research for causal investigations, while many qualitative researchers have rejected the concept of causation entirely. However, a growing number of scholars, in both research methods and philosophy, have proposed an alternative perspective, one that sees quantitative and qualitative approaches as having complementary strengths and limitations in understanding causation. In this article, we consider this perspective in relation to the study of causality in psychotherapy research. Method: This paper reviews and integrates key descriptions of the mechanisms for identifying causal processes using qualitative research. Results: An overview of how qualitative methods study causation is presented, considering its implications for both identifying causality and for generalizing causal conclusions. Conclusion: The paper holds relevance for establishing outcomes caused by psychotherapy treatments and for developing clinical practice guidance for the field.