Outcome criteria, measurement instrument, assessment points
| Outcome/variable | Instrument | Assessment point | ||
| T0 | T1 | T2* | ||
| Primary outcome | ||||
| Somatic symptom distress | PHQ-15 | x | x | x |
| Psychological and behavioural aspects of somatic symptom distress | SSD-12 | x | x | x |
| Secondary outcome | ||||
| Depression | PHQ-9 | x | x | x |
| Anxiety | GAD-7 | x | x | x |
| Functioning | PDI | x | x | x |
| Health anxiety | mSHAI | x | x | x |
| Attitude towards face-to-face psychotherapy | ATSPPH | x | x | x |
| Covariates | ||||
| Demographics | Web-based self-report | x | ||
| Healthcare utilisation | Web-based self-report | x | x | x |
| Somatosensory amplification | SSAS | x | ||
| Emotional reactivity | ERS | x | ||
| Therapeutic alliance | WAI-SR | (x) † | ||
| Attitudes and expectations towards iCBT | CEQ | x | ||
| Intervention satisfaction | CSQ-I | x ‡ | x | |
| Subjective negative intervention effects | INEP | x ‡ | x | |
| Adherence | Attrition/completion rates | x ‡ | x | |
*Only for control group.
†3 weeks after intervention start.
‡Only for intervention group.
T0, baseline; T1, 8 weeks postrandomisation; T2, 16 weeks postrandomisation; ATSPPH, Attitudes Towards Seeking Professional Psychological Help; GAD-7, Generalised Anxiety Disorder Questionnaire; INEP, Side Effects of Psychotherapy Inventory; mSHAI, modified short version of the Health Anxiety Inventory; PERS, Perth Emotion Reactivity Scale; PDI, Pain Disability Index; PHQ, Patient Health Questionnaire; SSAS, Somatosensory Amplification Scale; SSD-12, somatic symptom disorder—B Criteria Scale; WAI-SR, Working Alliance Inventory—short revised; CEQ, Credibility/Expectancy Questionnaire; CSQ-I, Client Satisfaction Questionnaire for internet-based interventions.