| Year | Value (SE) |
|---|---|
| 2000 | 0.2720 (0.0572) |
| 2001 | 0.0290 (0.0101) |
| 2002 | 0.3860 (0.1077) |
| 2003 | 0.4100 (0.0520) |
| 2005 | 0.2960 (0.0710) |
| 2007 | 0.5160 (0.0835) |
| 2008 | 0.7720 (0.1013) |
| 2010 | 0.5600 (0.0747) |
| 2012 | 0.4980 (0.0682) |
| 2013 | 0.7210 (0.1425) |
| 2015 | 0.4430 (0.1142) |
| 2019 | 0.4960 (0.0952) |
