Sources mentioned in the article draft (for verification/context):
- OECD Fiscal Decentralisation Database: https://www.oecd.org/tax/federalism/fiscal-decentralisation-database.htm
- U.S. GAO page on federal grants: https://www.gao.gov/federal-grants-state-and-local-governments

Reminder:
Exact definitions of “central” vs “regional” revenue can vary by dataset (e.g., consolidation rules, treatment of social security, and shared taxes).
