Processes between therapy sessions, so-called intersession processes, refer to the mental representations that patients have of their psychotherapy with their therapist. The underlying premise is that patients spend only 0.8% of their weekly waking time in psychotherapy sessions (Hartmann, 2003) – the effects of a session should therefore extend beyond this short duration. There is now increasing evidence that these intersession processes play a significant role in the internalization of psychotherapeutic processes and can predict therapeutic outcomes (Hartmann et al., 2010; Zeeck et al., 2016; Stewart & Schröder, 2015).

The instrumental retrieval of these mental representations appears to play a particularly important role in reducing distress and promoting well-being between sessions (Geller and Farber, 1993; Kaiser & Laireiter, 2019).

For a systematic and robust theoretical construction of intersession processes and their relationship to therapeutic outcomes, we apply Boorsboom's Theory Construction Methodology (TCM) (2021). Using the resulting formal model, we aim to identify the causal relationships and the role of intersession processes as a transtheoretical mechanism of action in psychotherapy. The various theoretical assumptions of the formal model are tested using Bayesian networks, and the underlying theory is optimized based on these findings.

The goal is to develop targeted clinical recommendations for promoting favorable intersession processes and reducing unfavorable ones, based on this theoretical foundation. Therefore, within our routine outcome monitoring and feedback system, GPNS, ​​intersession processes are recorded weekly before the start of each session and reported back to the therapists.