| Year | Value (SE) |
|---|---|
| 2000 | 0.4964 (0.0515) |
| 2001 | 0.4817 (0.0087) |
| 2002 | 0.5165 (0.0179) |
| 2003 | 0.5333 (0.0354) |
| 2004 | 0.4339 (0.0293) |
| 2005 | 0.4444 (0.0245) |
| 2006 | 0.4369 (0.0217) |
| 2007 | 0.5833 (0.0269) |
| 2008 | 0.5270 (0.0312) |
| 2009 | 0.5493 (0.0350) |
| 2010 | 0.5613 (0.0712) |
| 2011 | 0.4212 (0.0303) |
| 2012 | 0.5715 (0.0283) |
| 2013 | 0.6603 (0.0767) |
| 2014 | 0.5478 (0.0484) |
| 2015 | 0.4551 (0.0843) |
| 2016 | 0.5341 (0.0310) |
| 2019 | 0.4613 (0.0710) |
| 2020 | 0.4863 (0.1510) |
| 2021 | 0.5661 (0.4261) |
| 2022 | 0.4174 (0.2209) |
| 2023 | 0.3295 (0.0556) |
