  Background: The collective browsing behavior of users gives rise to a flow
network transporting attention between websites. By analyzing the structure of
this network we uncovered a nontrivial scaling regularity concerning the impact
of websites.
  Methodology: We constructed three clickstreams networks, whose nodes were
websites and edges were formed by the users switching between sites. We
developed an indicator Ci as a measure of the impact of site i and investigated
its correlation with the traffic of the site Ai both on the three networks and
across the language communities within the networks.
  Conclusions: We found that the impact of websites increased slower than their
traffic. Specifically, there existed a scaling relationship between Ci and Ai
with an exponent gamma smaller than 1. We suggested that this scaling
relationship characterized the decentralized structure of the clickstream
circulation: the World Wide Web is a system that favors small sites in
reassigning the collective attention of users.
