Table 1 Inclusion criteria^a

I-1

Population: Children and/or adolescents < 21 years of age with a mental disorder diagnosis with ICD-10 [21] or DSM-5 [22] (or previous versions) or other criteria valid enough that a diagnosis of a mental disorder could be reliably assumed at baseline^b.

I-2

Experimental intervention: Treatment with a psychotherapeutic intervention that can be attributed to systemic therapy. The experimental intervention was either purely systemic or systemic-integrative (contains both systemic and not clearly systemic components), with systemic elements predominating.

I-3

Comparison (control intervention): cognitive behavioural therapy. The control intervention included either only CBT or both CBT and non-CBT components (with CBT components predominating).

I-4

Outcome: Patient-relevant outcomes such as mortality, morbidity (symptoms, hospitalisation, and overall functioning, adverse events) or health-related quality of life were analysed.

I-5

Design: randomised controlled trial; there was no restriction regarding study duration.

I-6

Language: For non-German and non-English publications, an English-language title or abstract showing the relevance of the study had to be available.

I-7

Full publication available: In this context, a full publication also includes a study report in accordance with ICH E3 [28] or a study report meeting the criteria of the CONSORT statement [29] and allowing an assessment of the study, providing that the information on the study methods and results contained in these documents was not confidential.