Caldarelli, Guido and Chessa, Alessandro and Pammolli, Fabio and Pompa, Gabriele and Puliga, Michelangelo and Riccaboni, Massimo and Riotta, Gianni A multi-level geographical study of Italian political elections from Twitter Data. PloS One, 9 (5). e95809. ISSN 1932-6203 (2014)