Those of you who work in the areas of international relations and comparative politics are probably aware that there are several ways used to measure whether a country is a democracy or not, and the strength of that democracy. The most common measures are the Polity and Freedom House scores, but there are several others, including, prominently, the Democracy-Dictatorship method associated with Przeworski, Alvarez, Cheibub, Limongi, Gandhi, Vreeland, etc.
Cheibub, Gandhi and Vreeland have recently published a piece in Public Choice in which they make a very convincing case that Polity and Freedom House are both fundamentally flawed, and these two measures should usually be avoided in favor of the DD measure. If you do comparative politics, this is essential reading. If nothing else, many studies based on Polity measures probably need to be replicated using DD to see how the results stand up.
Also, you should check out Munck and Verkuilen 2002 for more on the problems of measuring democracy.