SynTrustBench: An Evidence-Gated and Executable Benchmark for Trustworthiness Claims in Synthetic Clinical Data

Synthetic clinical data are increasingly used for healthcare machine-learning development, model validation, data sharing, and predeployment testing, yet such data often claim to be trustworthy after passing a limited collection of realism tests. A synthetic dataset may indeed claim statistical similarity while leaking training membership, erasing rare subgroups, failing on held-out real patients, or lacking sufficient artifacts for reproduction. We introduce SynTrustBench, an evidence-gated and executable benchmark for evaluating trustworthiness claims across five non-compensable dimensions: fidelity, clinical utility/validity, privacy, equity, and robustness/generalization. Its Evidence Assessment component audits published reports and produces a five-element Evidence Maturity Profile (EMP) together with a separate evaluability gate. Its executable structured-tabular protocol accepts frozen real training data, held-out real test data, a synthetic table, and a declarative configuration; computes dimension-specific metrics and uncertainty; and produces subgroup results, failure flags, benchmark cards, and provenance manifests. In a frozen pilot audit of 30 reports, 17 of 30 quantitatively evaluated privacy, 2 of 30 documented a formal privacy guarantee to the audit threshold, 2 of 30 evaluated equity, 12 of 30 evaluated robustness, and only 4 of 30 passed the evaluability gate. The executable implementation operationalizes the same dimensions through distribution and dependency checks, frozen train-on-real/test-on-real (TRTR) and train-on-synthetic/test-on-real (TSTR) utility, empirical privacy attacks, subgroup analysis, perturbation testing, and a controlled failure-injection harness. SynTrustBench does not certify clinical safety or collapse trustworthiness into a single score. Instead, it provides an inspectable predeployment contract for identifying what was evaluated, what failed, what remains unknown, and whether evidence is sufficiently complete and reproducible for comparison or downstream healthcare AI use.