| Year | Value (SE) |
|---|---|
| 2008 | 0.8960 (0.0648) |
| 2009 | 0.9990 (0.0202) |
| 2010 | 0.9160 (0.0370) |
| 2011 | 0.9830 (0.0232) |
| 2012 | 0.9650 (0.0165) |
| 2013 | 0.9430 (0.0272) |
| 2014 | 0.9640 (0.0255) |
| 2015 | 1.0950 (0.0769) |
| 2016 | 1.0160 (0.0248) |
| 2017 | 1.0430 (0.0344) |
| 2018 | 1.0140 (0.0240) |
| 2019 | 0.9660 (0.0266) |
| 2020 | 0.9720 (0.0714) |
| 2021 | 0.9150 (0.1213) |
| 2022 | 1.0910 (0.1174) |
| 2023 | 1.0290 (0.0540) |
| 2024 | 0.8270 (0.1079) |
