Assessing the Mechanism of Change of Functional Analytic Psychotherapy: An Exploratory Analysis of a Process-Based Behavioral Intervention

Abstract

Identifying why and how psychological interventions work is one of the core areas of development in the current agenda of empirically based interventions. A process-to-outcome research approach was employed to examine the treatment effects and mechanism of change of Functional Analytic Psychotherapy (FAP), a process-based intervention focused on enhancing interpersonal repertoires. A non-concurrent multiple baseline design was conducted to evaluate the effects of FAP in three clients presenting with clinically relevant levels of psychological distress and interpersonal difficulties. FAP’s claimed mechanism of change (contingencies of reinforcement) was evaluated by assessing the probability with which therapists provided behavioral procedures (TCRBs) following clients’ responses in session (CRBs). Probabilities of contingent reinforcement were calculated through a lag sequential analysis. Between-Case Standardized Mean Difference (BC-SMD), Simulation Modeling Analysis (SMA), and Non-Overlap Analysis of all Pairs (NAP) tested between and within participants treatment effects. Results showed that high levels of contingent reinforcement (i.e., probabilities above 60%) were responsible for clinical changes on psychological distress and interpersonal difficulties. No moderation effects of therapeutic relationship factors such as therapeutic alliance and therapeutic relationship intimacy on treatment outcomes were observed. Limitations associated with reliability on the data collection level, coding, and design are discussed. Recommendations for replication and extension in other contexts and population are also presented. The role of interpersonal competence on psychological distress and an explanatory process-to-outcome model of FAP is summarized.