by Gene Callahan
On his blog, Daniel Kuehn notes that “relations in economies are not stable.” In fact, we can go further: Relations in the social sciences are not stable. As an illustration, consider Zipf’s Law as applied to city size.
In 1700, London had about 575,000 people. According to Zipf’s Law, the next-sized city should have had about 280,000 or 290,000 thousand. What was the actual size of the second largest city? As far as I can determine, it was Norwich, with a population of about 30,000. (My source for the population figures is 1688: The First Modern Revolution.) Zipf’s “Law” is off by a factor of about ten in this instance.
What I suspect is that there is some historical circumstance that leads to Zipf’s Law applying to city size in recent centuries, which was not present in 1700. As political scientist Terry Nardin put it: “Generalizations about how people usually behave are not scientific generalizations about a truly time-independent class of phenomena; they are more or less well-disguised descriptions of customs specific to a particular historical situation.”