Q. Political regime classification?

• Start with the Database of Political Institutions. Presents institutional and electoral results data such as measures of checks and balances, tenure and stability of the government, identification of party affiliation and ideology, and fragmentation of opposition and government parties in the legislature, among others.
• Also see V-DEM - Varieties of Democracy (1789+).  Multidimensional and disaggregated dataset that reflects the complexity of the concept of democracy as a system of rule that goes beyond the simple presence of elections. Distinguishes between electoral, liberal, participatory, deliberative, egalitarian, majoritarian and consensual, and collects data to measure these principles.

For more detail and sources, see the Politics Resource Guide.