Table 3.

Common themes and participant quotes from qualitative interviews.

Topics explored	Main themes (number of themes endorsed)	Participant quotes
Attitudes toward using technology	Participants were comfortable using technology in all aspects of daily life (7/8) Positive attitudes about using an app in treatment (5/8) Technology needs to be personalized to a person’s needs (3/8)	“It is good idea as I have my mobile with me all the time” (participant 2) “Using a phone is better than paper because it is easier to remember and register” (participant 4)
Experience of dialectical behavior therapy treatment	Positive experience (7/8) Treatment provided insight and skills to cope with difficulties (6/8)	“DBTa was great, I have learned lots of skills to use in my daily life, I am more calm and I do not have such a bad temperament now” (Participant 4) “ I have learnt about myself and I found out why I act in the way I do and when I feel bad what I can do to make it better” (Participant 5)
Relationship with therapist	There was a good relationship where patients felt safe and understood (7/8)	“It (our relationship) has been really good, I have been to many psychologists where I wasn’t understood but I was told there is something wrong with me. But now there was someone who finally understood me and helped me develop another perspective of myself” (participant 4)
Experience of using the app in treatment	It was easy to access when needed (5/8)	“It was really good because you are focused in another way. You are more aware what can fool you and how you can use the skills you have learnt (participant 1) “As soon as discover I have used a skill, so could open the app and register it. I didn’t need to remember I had used that skill” (participant 7)
Useful parts of app in dialectical behavior therapy treatment	The app was useful in recording mood and use of skills (7/8) The app was useful in recording reflection (5/8)	“I have more awareness of the specific skills that can help me if I am in a situation that is difficult to cope with. If I had an argument with my girlfriend, I could take a break and read in the app what I need here so I don’t switch over to an old response” (participant 1) “I can register my mood, feelings and one has notes where you can write what you have done during the day and remember how you have used the skills and how your mood has been” (participant 6)
The use of the app and impact on relationship with therapist	The app provided a common base and promoted collaboration when examining and discussing problematic situations (6/8)	“The app allowed my therapist to follow how I am going and to provide support if required. It provided us with a common overview of what we can examine and discuss together” (participant 6) “The app helped me work better with better with my therapist as she could quickly get insight into how I have been and we had more time to discuss things that were important rather than I have to try and remember the all difficulties I have had” (participant 8)
Advantages of using the app in dialectical behavior therapy treatment	The functions of the app were easily accessible (8/8) It helped patients be more aware of treatment issues inside and outside of therapy (5/8) Patients could access skills when they needed them (5/8)	“I am more aware of the skills and it does not require so much effort to take out my mobile phone discretely and use them” (participant 6). “I can see what I have done hangs together with my feelings” (participant 3) “I am aware of what skills I used yesterday and what I should use today” (participant 4)
Challenges using the app in treatment	The app should function without major problems and ITb support should be available (6/8) There are some technical challenges (2/8) and lacks some flexibility (3/8)	“The scroll function is irritating so it can take a long time to find the part of the app you want” (participant 3) “There are things on the app that are irrelevant” (participant 5) “It can be hard to add your own notes and find them again” (participant 6)

^aDBT: dialectical behavior therapy.

^bIT: information technology.