"Who Governs matters greatly to welfare state policy. An almost complete neglect of the parliamentary opposition in the comparative political economy suggests that only office-holding matters, but we disagree. We argue that opposition parties of the Left constrain Right governments' welfare state policies, while opposition parties of the Right have no similar effect on Left governments. This is the asymmetric opposition-government response mechanism. Through the compilation of an extensive dataset, we test the mechanism across 23 countries from 1980 to 2007 and find strong evidence for the existence of the mechanism. This demonstrates that parties matter to policy formation not only as yielders of office power, but as agenda setters too."

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