Very cool. Although, maybe another possible explanation is that people get "tired" at reading a whole page and skip to the next page, resulting in a top of the page bias. Also, love the use of R. R is beautiful.
R is awful. It's full of decisions made by people who seem to not have much programming experience, in that they seem good at the time but cause major issues later on. See, for instance, http://www.talyarkoni.org/blog/2012/06/08/r-the-master-troll... , http://blog.revolutionanalytics.com/2008/12/use-equals-or-ar... , http://shape-of-code.coding-guidelines.com/2012/02/29/parsin... , and the necessity of http://tim-smith.us/arrgh/ (I wrote up some stuff about the *apply functions, but not yet in a form suitable for the guide: https://github.com/tdsmith/aRrgh/issues/18 ) .