Philosophy professor Gary Gutting gets to the heart of the problem with economics and other social sciences.

While the physical sciences produce many detailed and precise predictions, the social sciences do not.  The reason is that such predictions almost always require randomized controlled experiments, which are seldom possible when people are involved.

His conclusion:

Given the limited predictive success and the lack of consensus in social sciences, their conclusions can seldom be primary guides to setting policy.  At best, they can supplement the general knowledge, practical experience, good sense and critical intelligence that we can only hope our political leaders will have.

via How Reliable Are the Social Sciences? – NYTimes.com.