Development and formative application of the Health Data Readiness Level framework for federated health-data services.

Objectives: To develop a multidimensional framework for assessing organisational and system readiness for federated health-data services, and to report its formative application across three heterogeneous UK ecosystems. Methods: The Health Data Readiness Level (HDRL) framework was developed from a structured landscape review of 56 maturity and readiness frameworks, first-principles requirements analysis, artificial-intelligence-assisted synthesis with human source verification, and stakeholder refinement. It comprises 64 indicators in eight domains and five ordered levels. Formative application examined three heterogeneous UK health-data research ecosystems using documentary evidence, professional stakeholder input, workshops, a structured right-of-reply process, cross-case calibration, and two illustrative research use cases. Analysis was descriptive; the application was not designed as psychometric validation or a league table. Results: All 64 indicators were scoreable in each case. Publicly reported profiles ranged from Developing (Level 2 -3) to Managed (Level 3 -4); all three cases met the proposed minimum for five foundational indicators. Recurring constraints concerned evidence of measured service performance, national-scale primary-care data access, cross-jurisdiction governance reciprocity, workforce capacity, and sustainable funding. Pandemic-era four-nation research was delivered through coordinated local analyses and meta-analysis, rather than routine automated federation. Discussion: HDRL operationalises a broad service- and system-readiness view that complements technical and governance specifications. Content validity, inter-rater reliability, aggregation choices, responsiveness and predictive validity remain to be established. Conclusion: HDRL is an evidence-informed candidate improvement and planning instrument for federated health-data services. It should not yet be used as an accreditation standard or as an official participation threshold for the UK's Health Data Research Service.