Many important policies are implemented at the national level. Monetary policy, fiscal policy, and many regulations are key examples. Pure time series or before-after analysis of the impacts of changes in these policies on the economy of a country will be contaminated by other changes going on in the economy. Simply trying to difference out global trends will not account for systematic differences in the growth path of the country where the reform took place from the average global growth path. This makes evaluation of the impacts of such policies difficult.
So I come back from vacation to find out that I was part of a randomized experiment in my absence. No, this had nothing to do with the wonders of airline travel in Europe (which don’t add that frisson of excitement through random cancellations like their American brethren), but rather two of our co-bloggers trying to figure out if the blog actually makes people recognize me and Jed more (here are links to parts