| Years | Relevant Studies | Selected Studies | Percentage |
| 2002 | 4 | 1 | 1.8 |
| 2003 | 5 | 2 | 3.5 |
| 2004 | 3 | 2 | 3.5 |
| 2005 | 11 | 3 | 8.9 |
| 2006 | 3 | 1 | 1.8 |
| 2007 | 7 | 4 | 7.1 |
| 2008 | 6 | 4 | 7.1 |
| 2009 | 22 | 4 | 7.1 |
| 2010 | 32 | 7 | 17.8 |
| 2011 | 14 | 4 | 7.1 |
| 2012 | 23 | 5 | 8.9 |
| 2013 | 18 | 6 | 10.7 |
| 2014 | 14 | 6 | 10.7 |
| 2015 | 12 | 7 | 17.8 |
| Total | 162 | 56 |
|