US government revenue: 11%, 26% or 30% of GDP?

The three series measure three nested objects: the World Bank counts central-government tax revenue only — no states, no cities, no social-security contributions (10.9%); the OECD counts taxes at every level of government including compulsory social contributions (25.6%); the IMF counts all general-government revenue, adding non-tax income such as fees and dividends (29.9%). Each is a correct answer to a different question about the size of the American state.