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<strong>Document</strong><br />

Page 43<br />

in economics. I can't resist showing you one example: Zipf's law, otherwise known as the rank-size rule.<br />

The "law" is an assertion about the distribution of city sizes, taking the form<br />

where N is the population of city j, R its rank (so that for the United States, New York is 1, Los Angeles<br />

2, Chicago 3, and so on), and b is an exponent close to 1. In hard science one is always finding relations<br />

like this, which then serve as a challenge for theorists. In social science they are rare. But just look at it<br />

(see figure 2.1).<br />

By the way, if you think that I am going to wrap up this lecture by showing how modern theory can<br />

explain Zipf's<br />

Figure 2.1<br />

<strong>file</strong>:///<strong>D|</strong>/Export2/<strong>www</strong>.<strong>netlibrary</strong>.<strong>com</strong>/<strong>nlreader</strong>/<strong>nlreader</strong>.<strong>dll</strong>@bookid=409&<strong>file</strong>name=page_43.html [4/18/2007 10:30:13 AM]

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