The cross-country comparative approach provides a number of unique advantages over national studies: It can exploit institutional variation that does not exist within countries; draw on much larger variation than usually available within any country; reveal whether any result is country - specific or more
general;
test whether effects are systematically heterogeneous in different settings; circumvent selection issues that plague within - country identification by using system - level aggregated measures; and uncover
general -
equilibrium effects that often elude studies in a single country.