| Year | Value (SE) |
|---|---|
| 2008 | 0.9160 (0.0569) |
| 2009 | 0.9730 (0.0269) |
| 2010 | 0.9320 (0.0595) |
| 2011 | 0.9140 (0.0145) |
| 2012 | 0.8820 (0.0159) |
| 2013 | 0.9570 (0.0414) |
| 2014 | 0.9260 (0.0208) |
| 2015 | 1.2500 (0.0880) |
| 2016 | 1.0010 (0.0226) |
| 2017 | 0.8520 (0.0293) |
| 2018 | 0.9570 (0.0378) |
| 2019 | 0.8980 (0.0309) |
| 2020 | 0.7550 (0.1586) |
| 2021 | 0.5690 (0.1597) |
| 2022 | 0.4700 (0.0623) |
| 2023 | 0.9610 (0.1031) |
