The goal of this feasibility study is to test whether a new blended digital intervention for adolescents with anxiety disorders is feasible and acceptable for use, and to help plan future larger scale studies. The main questions it aims to answer are:

• A: Can the investigators recruit appropriate participants?
• B: How appropriate are the data collection procedures and outcome measures?
• C: Are the study procedures and interventions suitable for and acceptable to the participants?
• D: Does the research team have the resources and ability to manage the study and intervention?
• E: Does the intervention show promise of being successful for adolescents with anxiety disorders?

Participants will:

• Receive outpatient anxiety treatment, typically every other week or weekly.
• Use the Sidekick app as a homework supplement to plan, carry out, and evaluate exposure exercises between treatment sessions.
• Complete questionnaires before, during, after, and three months after using the app.
• Some participants and therapists will be invited to take part in qualitative interviews following the intervention.

1. Study goals and objectives

   This project will investigate the feasibility of an app-facilitated exposure therapy for adolescents with anxiety. The primary objective is to contribute to the development of an efficient and personalized digital treatment. To meet this objective, the project aims i) evaluate the feasibility of Sidekick, a personalized digital treatment tool for patients with anxiety disorders, and ii) evaluate the user experience of digitally assisted exposure therapy on patient-clinician dyads.

   1.1 Short-term and long-term goals

   In the short-term, this project will implement an open, explorative trial of Sidekick in specialized clinical practice. In the long-term, the project will report, communicate and implement findings in clinical and user settings. If results indicate that the blended intervention is feasible and acceptable, the next step is to seek funding and perform a large-scale, national randomized controlled trials (RCT) of a blended treatment protocol for anxiety in adolescents.

2. Feasibility

2.1 Study design, choice of methodology and analysis

To meet the goals of this project, the investigators will conduct a single-arm feasibility trial of the app Sidekick in a blended intervention for anxiety disorders in adolescents. The open trial will include data from patients and their clinicians. The study will provide feasibility insights, determining the practicality of implementing the tool within the outpatient clinic. It will highlight usability and acceptance, as well as preliminary effectiveness of the app. User and therapist feedback will give insight into perceived benefits, challenges and suggestions for improvement, allowing for improved therapeutic options for adolescents with anxiety. The feasibility method and outcomes will be guided by Orsmond and Cohn "The Distinctive Features of a Feasibility Study: Objectives and Guiding Questions", and in line with the objectives, outcomes and interpretations of feasibility from Abbott and colleagues. Orsmond and Cohns highlights five objectives (A-E) that will be used as a template for assessing feasibility in our study. Our method for collecting data include questionnaires and user-data in the app from the patients, and qualitative interviews with both patients and clinicians. All outcomes will be reported in line with the CONSORT 2010 statement: extension to randomised pilot and feasibility trials, with adaptations to apply to our non-randomized feasibility trial.

2.1.1. Recruitment

The project aims to recruit 30 adolescents aged 13-18 from child and adolescent mental health services who, along with their clinicians, are willing to participate in the intervention as part of their treatment plan. All patient recruitment will be done in Helse Stavanger. The adolescents will receive gift cards of 250 NOK post assessment, and at 3-month follow-up. The adolescents that participate in qualitative interviews will receive an additional gift card of 250 NOK for their participation. Recruitment is set to begin in August 2025, with expected completion by the summer of 2026.

2.1.3 Procedures

Participants will first undergo a baseline assessment and be given guidance on how to use the Sidekick app to support anxiety exposure therapy. During the study period, all patients will be followed up through regular treatment at the Child and Adolescent Psychiatry Unit (BUP), which is usually weekly or bi-weekly. Patient responsibility and readiness will be maintained through this provider relationship as in regular treatment, but patients will also be provided with contact details for research personnel, who can then contact providers for the patients participating in the project. Exposure will mainly take place between treatment sessions, at times chosen by the youth themselves, or in collaboration with their clinician. Participants will undergo a baseline assessment online using the Youwell platform which is authorized for this purpose by Helse Vest. The assessment will be conducted at three timepoints: at baseline, at the end of treatment, and three months post-treatment. The feasibility and preliminary clinical outcomes of the intervention will be evaluated using quantitative methods before, during, and after the treatment. Additionally, qualitative interviews with therapists and patients will be conducted following the treatment to gather in-depth insights.

2.1.4 Interview guide

An interview guide will be used to gather data on participants' experiences, including perceived treatment. The interview guide will be developed in collaboration with users, and the interview is estimated to take 30 minutes to complete. Audio will be recorded using the app "Nettskjemadiktafon", which ensures safe storage of sensitive data. All data will be stored in TSD (in Norwegian, Service for Sensitive Data). The TSD service is designed for storing and post-processing sensitive data in compliance with the Norwegian "Personal Data Act" and "Health Research Act". Audio will be automatically transcribed using the service "Autotekst", and then manually checked by the PhD candidate.

2.1.5 Statistical analysis plan

As a feasibility study, no formal hypothesis testing will be conducted. Descriptive statistics will be used to summarize recruitment rates, retention rates, adherence, and data completeness to assess feasibility outcomes. Confidence intervals will be provided to estimate precision of feasibility parameters. Preliminary outcome measures will be explored to inform sample size calculations and study procedures for a future definitive trial. All analyses will be run using freely or commercially available software (R or SPSS statistics) by the applicant in collaboration with supervisors of the PhD-project. The sample size is based on recommendations for feasibility and pilot studies, recommending a sample size of 30 participants to establish feasibility.

2.1.6 Qualitative analysis plan

Using the NVivo software, qualitative data will be analyzed using thematic analysis to explore therapists' and users' experiences with the Sidekick app. Initial coding will capture key concepts, which will then be grouped into broader themes reflecting the core experiences of both therapists and adolescents. This process will highlight perceptions of the app, including its strengths and areas for improvement. Comparative analysis will contrast the themes from both perspectives to provide a comprehensive understanding of the app's impact and effectiveness in outpatient treatment. The findings will inform app enhancements and implementation strategies to better support therapists and adolescents in these settings.

Inclusion Criteria:

• 13 to 18 years old
• Adequate Norwegian reading, writing and speaking skills
• Access to the internett and a smart-phone
• Diagnosed anxiety disorder
• Receiving outpatient treatment for their anxiety disorder
• Exposure therapy included in therapy during the study period
• Therapist agrees to incorporate the app as an ad-on to therapy
• For patients receiving medication, inclusion requires a stable dose of medication for a psychiatric disorder for six weeks

Exclusion Criteria:

• Participants with serious mental illness, such as suicidality or poor general functioning may be excluded if participation is considered unfeasible or potentially harmful. Decision will be based on collaborative evaluation by the participants therapist and the research-team.