Both economists and political scientists have made important contributions to the field of public policy analysis. Economists have stressed the roles of competition, natural monopolies, information asymmetries, externalities, incentives, and federalism in promoting or undermining efficiency. Political scientists, in contrast, have focused more on the mechanics of agenda change, the likelihood of nonincremental policy change, and how the policy-making process varies across issue areas. Economists have influenced government decisions that led to the creation of public utility commissions, emissions trading, revenue sharing, and health maintenance organizations. Political scientists have influenced government decisions on the design of political institutions (environmental impact statements, legislative redistricting) and on the choice of public policies (criminal justice strategies, welfare reform). In general, the presence of a scholarly consensus facilitates the use of policy analysis. However, interest group politics and electoral incentives also play an important role.