| Year | Value (SE) |
|---|---|
| 2002 | 0.4629 (0.0500) |
| 2003 | 0.6275 (0.0658) |
| 2004 | 0.3412 (0.0757) |
| 2006 | 0.7054 (0.0348) |
| 2008 | 0.7372 (0.0690) |
| 2009 | 0.8226 (0.0583) |
| 2010 | 0.6791 (0.1292) |
| 2011 | 0.8669 (0.0839) |
| 2013 | 0.6830 (0.1166) |
| 2014 | 0.6377 (0.1064) |
| 2016 | 0.6793 (0.0687) |
| 2019 | 0.8359 (0.1368) |
