In this section we evaluate the robustness of the observed social effects phenomena by comparing review data from three additional different national Amazon sites: Amazon.co.uk (U.K), Amazon.de
(Germany) and Amazon.co.jp (Japan), collected using the same methodology described in Section 2, except that because of the particulars of the AWS API, we were unable to filter out mechanically
cross-posted reviews from the Amazon.co.jp data. It is reasonable to assume that these reviews were produced independently by four separate populations of reviewers (there exist customers who post reviews to multiple Amazon sites, but such behavior is unusual).