Primary outcomes and corresponding measures
| Primary outcome | Measure |
| Acceptability | |
| Patients’ satisfaction | 8-item Fragebogen zur Patientenzufriedenheit,81 the German adaptation of the 8-item Client Satisfaction Questionnaire,82 rated by patients at the end of treatment (T2) |
| Therapists’ satisfaction | Acceptability of Intervention Measure and Feasibility of Intervention Measure,83 two 5-item scales rated by therapists at the end of treatment (T2) |
| Negative psychological treatment effects | 32-item Negative Effects Questionnaire,84 rated by patients at the end of treatment (T2) |
| Adherence | Number of therapy sessions attended and number of intervention dropouts, determined by study personnel at the end of treatment (T2) |
| Feasibility | |
| Recruitment | Number of patients recruited per month (ie, recruitment speed) and percentage of suitable patients who agree to participate in the study (ie, recruitment rate), determined by study personnel at the end of treatment (T2) |
| Completeness of online data collection | Percentage of online questionnaires completed by patients and therapists before (T0), during (T1) and at the end of treatment (T2), determined by study personnel at T2 |
| Dropout rate | Number of patients terminating their study participation prematurely and their reasons for premature termination as assessed by the self-rated 25-item Reasons for Termination Scale85 |
| Quality of module-specific cut-off values | Percentage of patients receiving one, two or three modules (ie, module allocation rate), determined by study personnel at the end of treatment (T2) |
| Changes in psychopathology | |
| Self-rated severity of psychopathology | 53-item Brief Symptom Inventory,57 rated by patients at the end of treatment (T2) |
| Interviewer-rated severity of psychopathology | Global Assessment of Functioning,73 a 100-point scale rated by trained and blinded diagnosticians at the end of treatment (T2) |