Design and procedure

The study was conducted at a tertiary pain clinic and was an open pilot and feasibility study with two samples, one clinical and one self-referred. The clinical sample was recruited from the pain clinic between October 10 in 2015 and January 15 in 2017. These participants initiated treatment in five small consecutive cohorts between January 2016 and January 2017. The self-referred sample was recruited via ads in social media between September 23 and October 19, 2016 and started treatment in January 2017 (as one cohort). Inclusion criteria in both samples were persisting (continuous or recurrent) pain for more than 6 months, 18 to 65 years of age, ability to read and write in Swedish, access to a computer with internet, a personal cell phone and time to engage in treatment 20 minutes a day during treatment. Exclusion criteria were planned changes in pain medication, other planned medical interventions aiming at reducing pain, other cognitive behavioral therapy (CBT)/ACT interventions for the past 3 months at study start, and comorbid psychiatric or medical problems that required other care to be prioritized. Before inclusion participants were interviewed by a clinical psychologist specialized in pain. The interview contained a modified version of Mini International Neuropsychiatric Interview (using sections A–B, D–J, L–N) (30), as well as semi-structured questions on pain interference and pain related behavior. For the clinical sample this was done face-to-face, and for the self-referred sample via telephone. Participants were not reimbursed for participation in the study.