| Year | Value (SE) |
|---|---|
| 2006 | 0.8546 (0.0674) |
| 2007 | 0.9766 (0.1631) |
| 2008 | 0.6456 (0.0814) |
| 2009 | 1.0752 (0.0968) |
| 2010 | 1.0351 (0.1678) |
| 2011 | 1.0101 (0.0640) |
| 2012 | 0.8340 (0.0357) |
| 2013 | 1.0873 (0.1040) |
| 2014 | 0.8791 (0.0755) |
| 2015 | 1.1507 (0.2611) |
| 2016 | 0.8871 (0.0598) |
| 2017 | 0.9044 (0.0714) |
| 2018 | 0.9674 (0.0908) |
| 2019 | 0.9353 (0.1449) |
| 2020 | 0.7292 (0.2441) |
| 2021 | 1.3504 (1.0303) |
| 2022 | 0.7377 (0.1943) |
| 2023 | 0.8440 (0.1165) |
| 2024 | 0.4055 (0.1958) |
