| Year | Value (SE) |
|---|---|
| 2003 | 0.7980 (0.0765) |
| 2004 | 0.6620 (0.1288) |
| 2006 | 1.0650 (0.1248) |
| 2008 | 0.8110 (0.0786) |
| 2009 | 0.6840 (0.0777) |
| 2010 | 0.8360 (0.1016) |
| 2011 | 0.6790 (0.0305) |
| 2012 | 0.8920 (0.0663) |
| 2013 | 0.8110 (0.0483) |
| 2014 | 0.7830 (0.0367) |
| 2016 | 0.9400 (0.0347) |
| 2017 | 0.7760 (0.1167) |
| 2018 | 0.9030 (0.1417) |
| 2019 | 0.6000 (0.1787) |
