| Year | Value (SE) |
|---|---|
| 2000 | 0.4871 (0.0378) |
| 2001 | 0.4279 (0.0282) |
| 2002 | 0.7663 (0.0626) |
| 2003 | 0.7848 (0.0546) |
| 2005 | 0.7896 (0.0273) |
| 2007 | 0.7867 (0.0719) |
| 2008 | 1.0049 (0.0934) |
| 2010 | 1.3792 (0.2249) |
| 2012 | 0.8428 (0.0630) |
| 2013 | 0.9014 (0.1130) |
| 2015 | 1.0069 (0.2297) |
| 2019 | 0.7885 (0.0767) |
