Consider the following examples. Which is an example of a fuzzy RDD and which is a sharp RDD?
Running variable: Age. Treatment: You become eligible for senior citizen welfare programs once you are 65 are older.
Running variable: A region's poverty rate. Treatment: Regions become eligible for Federal assistance once their poverty rate is above a certain cutoff.
Running variable: Population. Treatment variable: Number of seats per state/province in a national government when each politician represents a different amount of citizens, like in the U.S. House of Representatives.