| Year | Value (SE) |
|---|---|
| 2000 | 0.5636 (0.0175) |
| 2001 | 0.7186 (0.0044) |
| 2002 | 0.6343 (0.0148) |
| 2003 | 0.6440 (0.0189) |
| 2004 | 0.5736 (0.0077) |
| 2005 | 0.4913 (0.0058) |
| 2006 | 0.5260 (0.0114) |
| 2007 | 0.6193 (0.0172) |
| 2008 | 0.6676 (0.0148) |
| 2009 | 0.6750 (0.0179) |
| 2010 | 0.7130 (0.0440) |
| 2011 | 0.5377 (0.0134) |
| 2012 | 0.5998 (0.0128) |
| 2013 | 0.7269 (0.0441) |
| 2014 | 0.7258 (0.0259) |
| 2015 | 0.5773 (0.0545) |
| 2016 | 0.6771 (0.0147) |
| 2019 | 0.5753 (0.0405) |
| 2020 | 0.5525 (0.0848) |
| 2021 | 0.5002 (0.1789) |
| 2022 | 0.5141 (0.0777) |
| 2023 | 0.5296 (0.0317) |
