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Authors
Olseth, Asgeir Røyrhus https://orcid.org/0009-0008-1213-3667
Høstmælingen, Andreas https://orcid.org/0000-0002-2513-1192
Bjørnebekk, Gunnar https://orcid.org/0000-0003-2176-7393
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Funding
Funding for this research was provided by:
NUBU - The Norwegian Center for Child Behavioral Development
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Article History
Received: 5 November 2025
Accepted: 30 January 2026
First Online: 10 April 2026
Declarations
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: This study was performed in line with the principles of the Declaration of Helsinki and approved by the Regional Committee for Medical Research Ethics South and East Norway (reference 2010/497).
: Informed consent was obtained from legal guardians for participants under 16 years of age, while participants aged 16 years and older provided informed consent on their own behalf. All youths were informed about the study and their right to decline or withdraw from participation at any time.
: The authors of this article declare the following potential conflicts of interest: Asgeir Røyrhus Olseth and Andreas Høstmælingen are currently employed at NCCBD, the organization responsible for the implementation of Functional Family Therapy in Norway from 2007 to 2024. Gunnar Bjørnebekk has no competing interests to declare that are relevant to the content of this article.
: The study design and hypotheses were reregistered in ISRCTN approximately one month after recruitment started; see .
