| Year | Value (SE) |
|---|---|
| 2008 | 0.5710 (0.0635) |
| 2009 | 0.6670 (0.0394) |
| 2010 | 0.6103 (0.0891) |
| 2011 | 0.6332 (0.0223) |
| 2012 | 0.5852 (0.0279) |
| 2013 | 0.4655 (0.0417) |
| 2014 | 0.5286 (0.0300) |
| 2015 | 0.5387 (0.1033) |
| 2016 | 0.6543 (0.0339) |
| 2017 | 0.6101 (0.0538) |
| 2018 | 0.5584 (0.0483) |
| 2019 | 0.3515 (0.0351) |
| 2020 | 0.5824 (0.2219) |
| 2021 | 0.4954 (0.3628) |
| 2022 | 0.6091 (0.2194) |
| 2023 | 0.3759 (0.0883) |
