| Year | Value (SE) |
|---|---|
| 2007 | 0.5355 (0.0415) |
| 2009 | 0.5806 (0.0264) |
| 2010 | 0.6938 (0.0412) |
| 2011 | 0.6402 (0.0191) |
| 2012 | 0.4897 (0.0130) |
| 2013 | 0.5492 (0.0256) |
| 2014 | 0.5409 (0.0163) |
| 2015 | 0.5772 (0.0834) |
| 2016 | 0.6300 (0.0208) |
| 2018 | 0.5960 (0.0507) |
| 2019 | 0.4967 (0.0318) |
| 2020 | 0.7502 (0.1632) |
| 2021 | 0.6855 (0.3145) |
| 2022 | 0.5458 (0.1999) |
| 2023 | 1.0535 (0.1561) |
