In Search of Lost Time: Discrete- Versus Continuous-Time Models of Working Alliance and Symptom Severity

Objective: The therapeutic alliance is one of the most stable predictors of symptom burden over the course of therapy. So far, this effect has only been examined on the basis of sessions. Continuous-time models (CTM) allow this relationship to be modeled as a continuous process in which the actual time interval between measurements is considered. The aim of the present study was to compare the fit of discrete-time models (DTM) of the alliance-symptom relationship with CTM using different time variables (sessions vs. actual time interval). Method: Data from 1,413 patients at a university psychotherapy outpatient clinic were analyzed. The alliance and symptom burden were assessed each session with the Bernese Session Report and the Hopkins Symptom Checklist-Short-Form, respectively. Different DTM and CTM were estimated using the R-package ctsem and compared in their fit via the Akaike information criterion. Results: CTMs with session as the time unit fitted the data best. Significant negative within-person effects of alliance and symptom burden were found. These effects showed a significant positive correlation, implying that individuals with a stronger effect of the alliance on symptom severity also showed a stronger effect of symptom severity on the alliance. Conclusions: When modeling the relationship of symptom severity and alliance, it seems to be of more importance to capture the fact that a session occurred than to capture the exact time intervals between sessions. Future studies should examine this finding for other psychotherapeutic factors. Interpersonal factors might explain the positive association of the reciprocal alliance-symptom effects.