| Year | Value (SE) |
|---|---|
| 2003 | 0.4732 (0.0460) |
| 2004 | 0.3509 (0.0686) |
| 2006 | 0.4729 (0.0565) |
| 2008 | 0.5474 (0.0533) |
| 2009 | 0.3789 (0.0432) |
| 2010 | 0.5493 (0.0668) |
| 2011 | 0.4088 (0.0184) |
| 2012 | 0.2221 (0.0167) |
| 2013 | 0.4509 (0.0270) |
| 2014 | 0.5050 (0.0238) |
| 2016 | 0.6439 (0.0240) |
| 2017 | 0.3810 (0.0573) |
| 2018 | 0.5355 (0.0825) |
| 2019 | 0.1434 (0.0419) |
