| Year | Value (SE) |
|---|---|
| 2000 | 0.4178 (0.0467) |
| 2001 | 0.2565 (0.0096) |
| 2002 | 0.4945 (0.0200) |
| 2003 | 0.4242 (0.0263) |
| 2004 | 0.3617 (0.0208) |
| 2005 | 0.3163 (0.0206) |
| 2006 | 0.2533 (0.0134) |
| 2007 | 0.4819 (0.0336) |
| 2008 | 0.5503 (0.0691) |
| 2009 | 0.4334 (0.0367) |
| 2010 | 0.4474 (0.0684) |
| 2011 | 0.4003 (0.0985) |
| 2012 | 0.5383 (0.0440) |
| 2013 | 0.5839 (0.0638) |
| 2014 | 0.5282 (0.0699) |
| 2015 | 0.5054 (0.1833) |
| 2016 | 0.4207 (0.0534) |
| 2018 | 0.4223 (0.0666) |
| 2019 | 0.4117 (0.0656) |
| 2020 | 0.4592 (0.1330) |
| 2021 | 0.2895 (0.2262) |
| 2022 | 0.4812 (0.2548) |
| 2023 | 0.2538 (0.0622) |
