| Year | Value (SE) |
|---|---|
| 2003 | 0.5930 (0.0424) |
| 2004 | 0.5300 (0.0854) |
| 2006 | 0.4440 (0.0280) |
| 2008 | 0.6750 (0.0404) |
| 2009 | 0.5540 (0.0464) |
| 2010 | 0.6570 (0.0738) |
| 2011 | 0.6020 (0.0151) |
| 2012 | 0.2490 (0.0122) |
| 2013 | 0.5560 (0.0234) |
| 2014 | 0.6450 (0.0184) |
| 2016 | 0.6850 (0.0142) |
| 2017 | 0.4910 (0.0629) |
| 2018 | 0.5930 (0.0683) |
| 2019 | 0.2390 (0.0569) |
