Linking process to outcome in Functional Analytic Psychotherapy: Evaluating the behavioral mechanism of change of a process-based therapy

Process-based therapy has received attention in recent years and seeks to advance our understanding of mechanisms of change in behavioral health interventions. A process-to-outcome research approach was employed to examine the mechanism of change and treatment effects of Functional Analytic Psychotherapy (FAP). A non-concurrent multiple baseline design was conducted with three clients who endorsed psychological distress and interpersonal difficulties. FAP's mechanism of change was tested with a lag sequential analysis. Statistical analysis for single-case designs was performed to assess between and within-participant treatment outcomes. High contingent and consistent reinforcement were associated with clinical changes in treatment outcomes. Therapeutic relationship factors such as therapeutic alliance and therapeutic relationship intimacy did not show moderation effects on treatment variables. Limitations and recommendations for improving reliability are discussed. The relations of treatment outcomes and FAP implementation are summarized. Finally, we discuss the relevance of process-to-outcome research for improving clinical science. • High contingent and consistent reinforcement reduce psychological distress. • A link between behavioral basic principles and clinical outcomes was observed. • Therapeutic alliance did not moderate treatment outcomes when implementing FAP. • Single-case designs aid the examination of mechanism of change and outcomes link.