Score contribution per author:
α: calibrated so average coauthorship-adjusted count equals average raw count
Residents both enjoy the policies adopted in their cities, and choose those policies. If some people can better evaluate policies than can others, then the most perceptive people will be the most willing to move to the city with better policies, thereby making that city more likely to adopt good policies in the future. Such migration can cause agglomeration, with some cities prospering and others failing.