The qualitative data were gathered at post-measurement through semi-structured telephone interviews that were audio-recorded and lasted 30 to 60 min. The interview guide (attached Appendix A) was prepared to allow for openness in the questions while at the same time covering the areas that prior research (i.e. qualitative studies investigating patients' experiences of guided internet-based self-help treatments) has shown to be central to the outcome of all psychological
treatments, e.g. expectations , alliance and feedback. One challenge was to allow for the interviews to capture experiences relating specifically to smartphone based therapy as well as other cognitive behavioral therapy -specific factors and general factors such as therapeutic alliance. In order to gain as rich information as possible, most questions were open-ended with subsequent follow-up questions. The qualitative method allowed for adjustments of the interview guide during the course of the study, as new questions arose. The validity of a qualitative study does not depend on all participants getting the exact same questions, but instead on the width and depth of the information gained. The interview guide was used rather as an inspiration than as a mandatory instrument. The interviews were recorded and transcribed to facilitate analysis. The interviewers, both clinical psychology students in their last term of a 5-year clinical program, and specifically trained to assess qualitative interviews, conducted and transcribed six interviews each. The interviewers were familiar with the original study, and were not blinded to the participants' outcome of the treatment.