Article PDF Filesizes

A small bit of my thesis. Why are BMC PDFs so significantly larger on average than PLOS or Zootaxa PDFs? data sources: A) 'Zootaxa' the entire set of articles published in the journal Zootaxa from 2001 to 2012 inclusive, consisting of 11563 pdf files downloaded direct from the publisher website : http://mapress.com/zootaxa/ B) 'PLOS' the entire set of articles published across 7 different PLOS journals: PLOS ONE, PLOS Biology, PLOS Computational Biology, PLOS Genetics, PLOS Medicine, PLOS Neglected Tropical Diseases, and PLOS Pathogens from 2003 to 2010-06-04, consisting of 20694 articles obtained via BioTorrents (Langille & Eisen, 2010). C) 'BMC' a subsample of 7948 open access articles containing the stemword 'phylogen*' at least once in the fulltext from the wide range of journals that BioMedCentral publish (the OA subset of this selection of papers: http://www.citeulike.org/user/testtest87)