| • Inclusion of long-term outcome variables such as abstinence and attendance of aftercare treatment programs |
| • Hierarchical data analysis |
| • Studies with randomized-controlled trial designs, and if randomization is not possible in the clinical context at least inclusion of a control group |
| • For all types of studies reports about characteristics of the interventions, studies and participation with transparent information about statistical procedures |
| • Reports of standardized effect sizes |
| • Inclusion of outcome variables related to skills (e.g., cognitive abilities), group dynamics and relationships (e.g., group cohesion, working alliance), and life quality and health (e.g., medical symptoms, general functioning) |
| • Use of standardized measurement instruments suitable for addiction and music therapy contexts |
| • Inclusion of external researchers who are not interventionists |
