Homophily and missing links in citation networks Valerio Ciotti, Moreno Bonaventura, Vincenzo Nicosia, Pietro Panzarasa and Vito Latora EPJ Data Sci., 5 1 (2016) 7 Published online: 03 March 2016 DOI: 10.1140/epjds/s13688-016-0068-2