| Year | Value (SE) |
|---|---|
| 2000 | 0.5404 (0.0233) |
| 2001 | 0.4551 (0.0068) |
| 2002 | 0.6138 (0.0126) |
| 2003 | 0.5098 (0.0149) |
| 2004 | 0.4856 (0.0063) |
| 2005 | 0.3768 (0.0057) |
| 2006 | 0.3366 (0.0077) |
| 2007 | 0.5601 (0.0209) |
| 2008 | 0.6092 (0.0252) |
| 2009 | 0.5259 (0.0184) |
| 2010 | 0.5604 (0.0401) |
| 2011 | 0.4881 (0.0359) |
| 2012 | 0.5772 (0.0206) |
| 2013 | 0.5925 (0.0229) |
| 2014 | 0.7149 (0.0362) |
| 2015 | 0.6043 (0.0971) |
| 2016 | 0.5672 (0.0286) |
| 2018 | 0.6360 (0.0269) |
| 2019 | 0.5234 (0.0327) |
| 2020 | 0.5034 (0.0640) |
| 2021 | 0.5341 (0.2039) |
| 2022 | 0.4283 (0.0567) |
| 2023 | 0.4796 (0.0478) |
