| Year | Coauthorship Index |
| 2006 | 2.6 |
| 2007 | 2.8 |
| 2008 | 2.4 |
| 2009 | 2.0 |
| 2010 | 2.2 |
| 2011 | 2.7 |
| 2012 | 2.0 |
| 2013 | 2.8 |
| 2014 | 2.5 |
| 2015 | 2.0 |