Cluster C personality disorders are fairly prevalent in clinical settings and are associated with impaired quality of life and high societal costs. Schema therapy aims to ameliorate the lives of clients by helping them change their dysfunctional schema mode activation patterns by healthier ways of behaving that lead to their needs being met.

This study sought to investigate whether 1) schema therapy is an effective treatment for cluster C personality disorders and 2) whether changes in the schema modes Vulnerable Child, Healthy Adult, Punitive Parent and Demanding Parent preceded change in the severity of the personality disorder and quality of life.

Data was collected at 5 timepoints from 269 participants receiving schema therapy across 10 mental health institutions in the Netherlands. Multilevel analyses were performed.

The results suggest that schema therapy was an effective treatment for cluster C personality disorders, with a significant decrease in symptom severity and a significant increase in quality of life having been observed. For some modes, its change preceded change in later symptom severity and quality of life, and for some modes there was a bidirectional relationship with symptom severity and quality of life.

The findings suggest that certain schema modes are important change mechanisms and that other modes have a more dynamic, reciprocal relationship with symptom severity and quality of life. The focus of current-day schema therapy on these schema modes seems justified, and future research is needed in order to better understand whether these relationships differ across specific personality disorders and schema therapy formats.