| Year | Value (SE) |
|---|---|
| 2003 | 0.4700 (0.0920) |
| 2004 | 0.2070 (0.0565) |
| 2006 | 0.3870 (0.0891) |
| 2008 | 0.5930 (0.1070) |
| 2009 | 0.3140 (0.0588) |
| 2010 | 0.5870 (0.0581) |
| 2011 | 0.5120 (0.0589) |
| 2012 | 0.1930 (0.0220) |
| 2013 | 0.3750 (0.0390) |
| 2014 | 0.4240 (0.0336) |
| 2016 | 0.5110 (0.0292) |
| 2017 | 0.4050 (0.0479) |
| 2018 | 0.5100 (0.0905) |
| 2019 | 0.1350 (0.0306) |
