| Year | Value (SE) |
|---|---|
| 2003 | 0.7932 (0.1718) |
| 2004 | 0.3912 (0.1305) |
| 2006 | 0.8712 (0.2242) |
| 2008 | 0.8799 (0.1798) |
| 2009 | 0.5664 (0.1237) |
| 2010 | 0.8937 (0.1399) |
| 2011 | 0.8515 (0.1048) |
| 2012 | 0.7734 (0.1050) |
| 2013 | 0.6748 (0.0806) |
| 2014 | 0.6569 (0.0602) |
| 2016 | 0.7454 (0.0506) |
| 2017 | 0.8257 (0.1576) |
| 2018 | 0.8606 (0.2036) |
| 2019 | 0.5628 (0.2104) |
