A policy considered in isolation may be ineffective because of the countervailing impact of other factors. And the success of a policy may itself lead to perverse incentives. Thus it is important to design complementary policies that support the original goal. Controlling air pollution from...

Findings of inverted-U relationships between income and certain types of pollution have generated considerable controversy, yet relatively little is known about the factors underlying these relationships. U.S. emissions of several major air pollutants have begun to decline, mirroring the...