| Year | Value (SE) |
|---|---|
| 2000 | 0.5209 (0.0408) |
| 2001 | 0.3777 (0.0087) |
| 2002 | 0.6052 (0.0159) |
| 2003 | 0.4242 (0.0225) |
| 2004 | 0.4176 (0.0156) |
| 2005 | 0.3244 (0.0108) |
| 2006 | 0.3059 (0.0104) |
| 2007 | 0.5848 (0.0362) |
| 2008 | 0.5720 (0.0410) |
| 2009 | 0.6053 (0.0399) |
| 2010 | 0.5307 (0.0747) |
| 2011 | 0.4114 (0.0409) |
| 2012 | 0.5097 (0.0271) |
| 2013 | 0.5653 (0.0384) |
| 2014 | 0.6441 (0.0562) |
| 2015 | 0.6357 (0.1966) |
| 2016 | 0.5292 (0.0467) |
| 2018 | 0.5088 (0.0398) |
| 2019 | 0.5009 (0.0457) |
| 2020 | 0.4475 (0.0962) |
| 2021 | 0.4940 (0.3751) |
| 2022 | 0.5777 (0.1386) |
| 2023 | 0.3990 (0.0623) |
