One of the authors here. That's correct. The spillover to other sites is not studied. Based on an (admittedly imperfectly) related paper with Stevie Chancellor

One of the authors here. That's correct. The spillover to other sites is not studied. Based on an (admittedly imperfectly) related paper with Stevie Chancellor & Munmun De Choudhury [1], I would expect that the spillover to other sites results in a 1) smaller, but 2) more committed group of users. http://comp.social.gatech.edu/papers/cscw16.thyghgapp.chancellor.pdf http://comp.social.gatech.edu/papers/cscw16.thyghgapp.chance... (see Summary of Findings, page 10)