RESUMEN
BACKGROUND: Schema therapy is effective for most outpatients with personality disorders (PDs). However, a subgroup does not sufficiently benefit from outpatient programmes. Despite its common clinical use, a thorough evaluation of day treatment group schema therapy (GST) is lacking. AIMS: This study aimed to investigate the effectiveness of day treatment GST for patients with PDs. METHODS AND PROCEDURES: Negative core beliefs were the primary outcome in a multiple baseline single-case design, measured weekly before and during 30 weeks of day treatment GST. Secondary outcomes included severity of primary PD, early maladaptive schemas (EMS), schema modes and general psychopathology measured before and after day treatment GST. Intervention effects were evaluated through visual inspection and randomization test analysis, with a reliable change index calculated for the secondary outcome measures. OUTCOMES AND RESULTS: A total of 79% of treatment completers showed a significant positive effect of day treatment GST with large effect sizes (Cohen's d: 0.96-10.04). Secondary outcomes supported these findings: 56% had a significant decrease in the severity of primary PD and 53% in general psychopathology. In addition, 63% of EMS and 72% of schema modes (87.5% for functional schema modes) showed significant positive reliable changes. CONCLUSIONS AND IMPLICATIONS: This is the first empirical study that demonstrated the effectiveness of day treatment GST in patients with severe PDs. Day treatment GST can serve as a stepped care treatment option for nonresponsive patients in outpatient programmes. Further randomized controlled (cost-)effectiveness research is necessary to substantiate these findings and investigate the specific patient populations for which day treatment is essential.