| Year | Value (SE) |
|---|---|
| 2008 | 0.8322 (0.0711) |
| 2009 | 0.8044 (0.0484) |
| 2010 | 0.7543 (0.1523) |
| 2011 | 0.7866 (0.0240) |
| 2013 | 0.7506 (0.1213) |
| 2014 | 0.8752 (0.1336) |
| 2015 | 0.6285 (0.2626) |
| 2016 | 0.7719 (0.0816) |
| 2017 | 0.7208 (0.0604) |
| 2018 | 1.0870 (0.2137) |
| 2019 | 0.8598 (0.1552) |
| 2020 | 0.6741 (0.3547) |
| 2021 | 0.6124 (0.2380) |
| 2023 | 0.5455 (0.1732) |
| 2024 | 0.8364 (0.4023) |
