When researchers study federalism in practice (de facto federalism), what measure do they use to estimate how centralized a country is?

Question

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The central government's share of tax revenue is the most commonly used measure to estimate how centralized a country is. A higher share of tax revenue controlled by the central government indicates a more centralized system, while a lower share indicates a more decentralized or federal system. The effective number of parties and the number of regional subunits are not directly related to centralization, but rather to the level of political competition and regional differentiation, respectively.

When Researchers Study Federalism in Practice (De Facto Federalism), What