SIBS-RCT is a randomized controlled trial comparing the effect of a 5-session group intervention for siblings and parents of children with chronic illness to 12-week waitlist. Participants randomized to waitlist will receive the intervention after waitlist. The main outcome is sibling mental health, and secondary outcomes include family communication, sibling disorder knowledge, quality of life, and adaption. Outcomes will be examined at pre-, post, 3-, 6- and 12- month follow-up.

Siblings' wellbeing is at risk when one's brother or sister has a neurodevelopmental disorder. Neurodevelopmental disorders are enduring somatic and/or mental conditions affecting the central nervous system, such as autism, intellectual disability, and cerebral palsy. The mechanisms behind the wellbeing risk for siblings are linked to siblings' lack of disorder knowledge, poor parental mental health due to extra care responsibilities, and impaired family communication. No evidence-based interventions to improve sibling wellbeing exist. To address this gap, we propose examining a group intervention for siblings and parents of children with neurodevelopmental disorders in a randomized controlled trial (SIBS-RCT). SIBS-RCT compares a 5-session manual-based sibling-parent group intervention delivered over two weeks, to 3-month "treatment as usual" waitlist. The planned sample is 288 siblings and 288 parents. Recruitment and intervention will take place in specialist and municipal health services. Inclusion criteria are being the sibling (aged 8-16 years) of a child (aged 0-18 years) who is diagnosed with neurodevelopmental disorder and who receives specialist or municipal health services. Participants will be randomized in blocks of 6 to intervention or waitlist. The primary outcome is sibling mental health. Secondary outcomes include quality of life, disorder knowledge, and family communication. Predictor measures include biological stress levels, parent mental health, disorder impairment, and group leader adherence to the SIBS-manual. Measures will be electronically rated by siblings, parents, and teachers at pre-intervention, post-intervention, and 3, 6, and 12 months follow-up. Main effects of the intervention will be measured as the mean mental health change difference between intervention and waitlist from pre-intervention to 3-month follow-up. We will also apply growth curve models to examine trajectories of outcomes from pre-intervention to 12-month follow-up. Expected outcomes include improved sibling wellbeing, improved health services for siblings and families of children with neurodevelopmental disorders, and better integration between municipal and specialist services.

Inclusion Criteria:

1. Being the sibling of a child diagnosed with chronic illness who is aged 0 to 18 years and receives specialist and/or municipal health services.
2. One parent able to attend the intervention.

Exclusion Criteria:

1. Being enrolled as primary patients in specialist health services;
2. Chronic illness diagnosis.

The scientific advisory board for this trial involves researchers from multiple sites, and de-identified data will be shared although details are not set.

N/A, not possible