Successful transfer of subspecialty care to continuous care from a prioritized subspeciality provider in adult care will be measured using a relational continuity of care measure - the Bice Boxerman Index.

Successful transfer of subspecialty care to continuous care from all subspecialty providers in adult care will be measured using a relational continuity of care measure - the Bice Boxerman Index.

The proportion of patients who receive a Bice Boxerman Index score of 0 (< 2 visits to both a subspecialty and primary care provider) will be assessed.

The proportion of visits to all primary care providers that are made to the usual care provider will be assessed among individuals who had ≥ 3 primary care visits (UPC Index).

The change in caregiver satisfaction with transitional health care services will be measured using the Larsen Client Satisfaction Questionnaire (CSQ) (8-item). The change in patient satisfaction will also be measured with the CSQ where able. Comparisons will be made between intervention and control groups.

The change in the caregiver's family empowerment status will be measured with the Family Empowerment Scale (24-item). Scoring will be accomplished by summing responses from items within the family (12 items) and service system (12 items) to generate sub-scores. Comparisons will be made between intervention and control groups.

The change in the patient's knowledge and confidence in managing their health will be measured (if able) using the Patient Activation Measure (10-item). Comparisons will be made between intervention and control groups.

The change in utility of care planning tools, written transition plan assessment, coordination of care among providers and families and, coordination of care between providers and families will be assessed with the Family Experiences with Coordination of Care (FECC) survey, completed by the caregiver. Comparisons will be made between intervention and control groups.

The number of patients who have received (presence or absence) adult-oriented funding and services will be assessed via report by the caregiver or, if able, the youth (e.g., receipt of Ontario Disability Support Program ODSP funding). Comparisons will be made between intervention and control groups.

Low acuity emergency department visits, emergency department use, hospitalization, technological complications, and immunization will be captured using encoded health administrative data housed at ICES to determine the patient's health care and preventative care use. Comparisons will be made between intervention and control groups.

A probabilistic cost-utility analysis will be conducted using patient-level data, to determine the incremental cost per quality-adjusted life-year gained (QALY) of intensive transition support compared to usual care, from a health system perspective. QALY gains for both patient and caregiver will be included. All direct health care costs and health service utilization will be ascertained from study data linked to administrative datasets at ICES. Utility, determined by mapping patient and caregiver responses to the EQ-5D-5L, will be used to generate QALY gains (or losses) over the time horizon.

The change in overall health-related quality of life of both the patient and their caregiver will be measured using the EQ-5D-5L. The digit for each of the scale's five dimensions (mobility, self-care, usual activities, pain/discomfort, and anxiety/depression) can be combined into a 5-digit number that describes the patient's health state and is commonly used to estimate health utilities. The descriptive system is complemented by a visual analogue scale where patients record their self-rated health. Comparisons will be made between intervention and control groups.

The change in caregiver fatigue will be measured using the PROMIS Fatigue Scale (8-item). The Fatigue scale is divided into the experience of fatigue (frequency, duration, and intensity) and the impact of fatigue on physical, mental, and social activities. Each question has five response options ranging in value from one to five. Comparisons will be made between intervention and control groups.

The change in family distress will be assessed using the Brief Family Distress Scale (1-item) completed by the caregiver. The 10-point Likert scale is used to measure crisis level, which is assigned by groupings of the scale continuum, with a level between 1-3 indicating no impairment, 4-5, moderate impairment, and 6-10, marked impairment. Comparisons will be made between intervention and control groups.

Semi-structured qualitative interviews will be conducted with a subset of intervention participants, health care providers, including both pre-transition and post-transition clinicians, and the transition team to gauge their experience with the transition support process.

The implementation process will be assessed by determining the fidelity of the intervention using percentages of completion for each of the four main intervention components. The percentage of primary care visits scheduled and attended by the transition team will be captured by the transition team for those participants assigned to the intervention group.

The implementation process will be assessed by determining the fidelity of the intervention using percentages of completion for each of the four main intervention components. The percentage of joint adult subspecialty visits and visits scheduled and attended by the transition team will be captured by the transition team for those participants assigned to the intervention group.

The implementation process will be assessed by determining the fidelity of the intervention using percentages of completion for each of the four main intervention components. The percentage of eligible funding applications completed and received will be captured by the transition team for those participants assigned to the intervention group.