| Year | Value (SE) |
|---|---|
| 2008 | 0.3189 (0.0405) |
| 2009 | 0.4337 (0.0217) |
| 2010 | 0.2525 (0.0685) |
| 2011 | 0.3701 (0.0132) |
| 2012 | 0.4391 (0.0158) |
| 2013 | 0.5669 (0.0464) |
| 2014 | 0.7026 (0.0347) |
| 2015 | 0.5497 (0.0983) |
| 2016 | 0.5128 (0.0378) |
| 2017 | 0.5635 (0.0543) |
| 2018 | 0.3447 (0.0506) |
| 2019 | 0.1607 (0.0269) |
| 2020 | 0.3601 (0.1277) |
| 2021 | 0.2293 (0.2721) |
| 2022 | 0.3996 (0.1478) |
