| Year | Value (SE) |
|---|---|
| 2008 | 0.9080 (0.1231) |
| 2009 | 0.8520 (0.0503) |
| 2010 | 0.7010 (0.0641) |
| 2011 | 0.8200 (0.0571) |
| 2012 | 0.9210 (0.0629) |
| 2013 | 0.7320 (0.0583) |
| 2014 | 0.7440 (0.0671) |
| 2015 | 0.7410 (0.1015) |
| 2016 | 0.9270 (0.0527) |
| 2017 | 0.9720 (0.0855) |
| 2018 | 0.9240 (0.0988) |
| 2019 | 0.8360 (0.0762) |
| 2020 | 0.7660 (0.1632) |
| 2021 | 0.8600 (0.2241) |
| 2022 | 0.9890 (0.2573) |
| 2023 | 0.7550 (0.1182) |
| 2024 | 1.4930 (0.6399) |
