| Year | Value (SE) |
|---|---|
| 2007 | 0.5630 (0.0303) |
| 2008 | 0.3310 (0.0205) |
| 2009 | 0.3604 (0.0136) |
| 2010 | 0.4270 (0.0321) |
| 2011 | 0.4986 (0.0119) |
| 2012 | 0.4262 (0.0099) |
| 2013 | 0.5540 (0.0191) |
| 2014 | 0.6910 (0.0191) |
| 2015 | 0.7685 (0.0737) |
| 2016 | 0.6753 (0.0153) |
| 2017 | 0.5626 (0.0170) |
| 2018 | 0.5528 (0.0283) |
| 2019 | 0.4324 (0.0289) |
| 2020 | 0.7454 (0.1233) |
| 2021 | 0.8025 (0.4328) |
| 2022 | 0.4216 (0.0458) |
| 2023 | 0.5194 (0.0282) |
| 2024 | 0.6199 (0.2054) |
