To track the spread of democracy around the globe, we used the ratings contained in the Center for Systemic Peace’s Polity IV dataset. Polity is a widely used resource in political science that ...

Democracy—measured by the Polity IV status —has rapidly spread around the globe. Vaccination against some of the worst killers of human history has become almost universal.

Polity IV assigns a score to each answer, then adds up a total score for that country ranging from 0 to 10. Freedom House assigns scores ranging from 1 to 7 for two categories each, civil ...