| Year | Value (SE) |
|---|---|
| 2000 | 0.5693 (0.0467) |
| 2001 | 0.6432 (0.0069) |
| 2002 | 0.6020 (0.0165) |
| 2003 | 0.5854 (0.0353) |
| 2004 | 0.5209 (0.0256) |
| 2005 | 0.4269 (0.0116) |
| 2006 | 0.4860 (0.0155) |
| 2007 | 0.6019 (0.0254) |
| 2008 | 0.5902 (0.0236) |
| 2009 | 0.7344 (0.0399) |
| 2010 | 0.7280 (0.0890) |
| 2011 | 0.5716 (0.0234) |
| 2012 | 0.5608 (0.0190) |
| 2013 | 0.7494 (0.0762) |
| 2014 | 0.6453 (0.0431) |
| 2015 | 0.6142 (0.1046) |
| 2016 | 0.5755 (0.0230) |
| 2019 | 0.5960 (0.0660) |
| 2020 | 0.6348 (0.1810) |
| 2021 | 0.6707 (0.4962) |
| 2022 | 0.6333 (0.1993) |
| 2023 | 0.4804 (0.0531) |
