| Year | Value (SE) |
|---|---|
| 2000 | 0.4248 (0.0331) |
| 2001 | 0.3380 (0.0225) |
| 2002 | 0.6069 (0.0500) |
| 2003 | 0.6993 (0.0488) |
| 2005 | 0.6554 (0.0233) |
| 2007 | 0.7505 (0.0686) |
| 2008 | 0.9054 (0.0843) |
| 2010 | 1.1778 (0.1922) |
| 2012 | 0.7812 (0.0585) |
| 2013 | 0.9996 (0.1251) |
| 2015 | 0.8548 (0.1950) |
| 2019 | 0.7262 (0.0710) |
