1. The Information School, University of Sheffield , The Wave, 2 Whitham Rd, Broomhall , Sheffield S10 2SJ, UK
2. Statistical Cybermetrics and Research Evaluation Group, Wolverhampton Business School, University of Wolverhampton , Wolverhampton WV1 1LY, UK
3. Lab of Physics in Economy and Social Sciences, Faculty of Physics, Warsaw University of Technology , Koszykowa 75 , 00-662 Warsaw, Poland