| Year | Value (SE) |
|---|---|
| 2003 | 0.3110 (0.0102) |
| 2004 | 0.3700 (0.0177) |
| 2005 | 0.2170 (0.0064) |
| 2008 | 0.3810 (0.0405) |
| 2009 | 0.2630 (0.0333) |
| 2010 | 0.5243 (0.0262) |
| 2011 | 0.3272 (0.0149) |
| 2012 | 0.3552 (0.0205) |
| 2013 | 0.4083 (0.0360) |
| 2014 | 0.4656 (0.0436) |
| 2015 | 0.3831 (0.0342) |
| 2016 | 0.4186 (0.0221) |
| 2017 | 0.5400 (0.0705) |
| 2018 | 0.6483 (0.1128) |
| 2021 | 0.1575 (0.0374) |
| 2022 | 0.1852 (0.0426) |
| 2024 | 0.2035 (0.1362) |
