Economic growth would be a socially easier process if it was smooth and even across society: that is, if most people could just get steady raises for doing their same jobs a little better each year. When growth benefits some and not others, or even benefits some while imposing losses and costs of transition on others, then controversies arise.

Arnold Harberger offered a nice metaphor thinking about this difference in his Presidential Address to the American Economic Association back in 1998, entitled \”A Vision of the Growth Process\” and published in the March 1998 issue of the American Economic Review.  Harberger discusses whether economic growth is more likely to be like \”mushrooms,\” in the sense that certain  parts of a growing economy will take off much faster than others, or more like \”yeast,\” in the sense that economy overall expands fairly smoothly overall. He argues that \”mushroom\”-type growth is more common. Harberger writes:

\”The analogy with yeast and mushrooms comes from the fact that yeast causes bread to expand very evenly, like a balloon being filled with air, while mushrooms have the habit of popping up, almost overnight, in a fashion that  is not easy to predict. I believe that a \”yeast\” process fits best with very broad and general externalities, like externalities linked to the growth of the total stock of knowledge or of  human capital, or brought about by economies of scale tied to the scale of the economy as a whole. A \’\’mushroom\’\’ process fits more readily with a vision such as ours, of real cost reductions stemming from 1001 different  causes, though I recognize that one can build scenarios in which even 1001 causes could  work rather evenly over the whole economy. Personally, I have always gravitated toward the \”mushrooms\” side of this dichotomy. I remember being impressed, when I first saw some early industry estimates of TFP [total factor productivity] improvement, by their tendency to industry concentration.\”

To put this another way, a lot of the policies for encouraging economic growth–like investing in human capital, technology, infrastraucture, and a supportive institutional environment for innovation–seem to suggest the possibility of broadly shared economic gains. But the economic growth that results will often be often mushroom-like and disruptive, affecting certain industries, localities, and kinds of workers more than others.

Paul Romer, who recently accepted the position of Chief Economist at the World Bank, recently  offered on his blog a summary of the social problem that then arises in a pithy aphorism: \”Everyone wants progress. Nobody wants change.\”

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