In his comment on my Mathiness paper, Noah Smith asks for more evidence that the theory in the McGrattan-Prescott paper that I cite is any worse than the theory I compare it to by Robert Solow and Gary Becker. I agree with Brad DeLong’s defense of the Solow model. I’ll elaborate, by using the familiar analogy that theory is to the world as a map is to terrain. There is no such thing as the perfect map.

In my Mathiness article, I refer to this quote from Lucas (2009): Some knowledge can be ‘embodied’ in books, blueprints, machines and other kinds of physical capital, and we know how to introduce capital into a growth model, but we also know that doing so does not by itself provide an engine of sustained growth. Ask yourself these three questions: 1. Which logical quantifier on the set of models does Lucas need to insert before “doing so does not …” to make the clause that follows the conjunction “but” true?

I have a new paper in the Papers and Proceedings Volume of the AER that is out in print and on the AER website. A short version of the supporting appendix is available here and on the AER website. A longer version with more details behind the calculations is available here. The point of the paper is that if we want economics to be a science, we have to recognize that it is not ok for macroeconomists to hole up in separate camps, one that supports its version of the geocentric model of the solar system and another that supports the heliocentric model.

The data presented here convinces me that policy-induced changes in the urban share of the population could have big effects on GDP per capita and could operate on a scale that affects the quality of life for billions of people. So in research on development policy, I am not persuaded that economists should narrow their focus to the analysis of such easily evaluated micro-initiatives as funding women’s self-help groups. Neither is Lant Pritchett.

My daughter, who is a pediatrician in California, sends the discouraging news that it is the best-educated parents who are leading the movement against vaccines. They should read this Rubella Has Been Eliminated From the Americas, Health Officials Say from the New York Times. Perhaps the most famous American rubella victim was the actress Gene Tierney. In 1943, newly pregnant, she volunteered to be in a show at the Hollywood Canteen, a film-industry nightclub for American troops.