“Based on the definition of the well-known h index we propose a t factor for measuring the impact of publications (and other entities) on Twitter. “The new index combines tweet and retweet data in a balanced way whereby retweets are seen as data reflecting the impact of initial tweets. The t factor is defined as follows: A unit (single publication, journal, researcher, research group etc.) has factor t if t of its Nt tweets have at least t retweets each and the other (Nt-t) tweets have ≤t retweets each.” [Authors – Lutz Bornmann, Administrative Headquarters of the Max Planck Society, Division for Science and Innovation Studies and Robin Haunschild, Max Planck Institute for Solid State Research – via arXiv, August 10, 2015]