| Year | Value (SE) |
|---|---|
| 2008 | 0.9950 (0.0926) |
| 2009 | 0.9060 (0.0459) |
| 2010 | 0.8760 (0.0779) |
| 2011 | 1.0590 (0.0322) |
| 2012 | 0.9520 (0.0223) |
| 2013 | 0.9410 (0.0510) |
| 2014 | 0.8850 (0.0431) |
| 2015 | 0.6590 (0.0912) |
| 2016 | 1.0680 (0.0540) |
| 2018 | 0.9440 (0.0568) |
| 2019 | 0.9290 (0.1018) |
| 2020 | 0.7320 (0.1299) |
| 2022 | 0.8810 (0.1470) |
| 2023 | 0.9490 (0.0787) |
