To Örebro University

Acceptance and Commitment Therapy has gained preliminary evidence for paediatric chronic pain. Several studies show that psychological flexibility/inflexibility is a process driving treatment change in ACT for chronic pain. The literature supporting psychological flexibility as a change process in ACT is typically based on selfreport. The aim of the present study was to investigate psychological flexibility (i.e. acceptance, defusion, values formulation and committed action) as in-treatment behaviour during internet-delivered Acceptance and Commitment Therapy for paediatric chronic pain, by having two independent observers rating patient written statements. The sample was self-recruited and consisted of 28 girls between ages 13 and 17 years. Results showed that psychological flexibility could be operationalised as in-treatment behaviours and reliably assessed using observer ratings. Also, data illustrated a within subject variability in ratings of acceptance and defusion, with a considerable difference in degree of acceptance or defusion evoked by different experiential exercises. Furthermore, analyses showed that a higher average degree of acceptance in patient statements during the early phase of treatment was related to larger treatment effects. Defusion, values formulation and committed action showed no significant influence on outcome. Results should be interpreted with caution due to the small sample size.