This paper answers the question posed in the title within a model where agents receive idiosyncratic, wage-rate shocks that are privately observed. When the model social insurance system is comprised by the US social security and income tax system, then the maximum ex-ante welfare gain to...

How far is the US social insurance system from an efficient system? We answer this question within a model where agents receive idiosyncratic, labor-productivity shocks that are privately observed. When social security and income taxation comprise the social insurance system, the maximum...