Synthetic Patients and What They Can and Cannot Teach: A Retrospective Analysis of Open-Source Contributions to Synthea

Retrospective analysis of 7 open-source pull requests to Synthea, the synthetic patient generator, extracted from the GitHub API on 4 November 2026. Six merged, one open, none closed unmerged. The merged work fixes a claim total that did not equal the sum of its items, a platelet distribution width range copied from a platelet count (150 to 520 instead of 9 to 17 fL, corrected in 9 module files), a null-unsafe comparison that could kill a FHIR export run, a file stream left open, string comparisons by identity, and undocumented configuration precedence. The open PR addresses duplicate primary keys in claim transaction exports at scale, reported with 10,000 patients and again with 1,000,000 patients. The paper's claim: synthetic patients teach pipeline shape, export format, and billing arithmetic well, and teach clinical outcomes badly, a limit confirmed by the validation literature (zero complications after hip/knee replacement and zero controlled blood pressures in a 1.2 million person synthetic population, against real rates near 3% and 70%).