| Year | Value (SE) |
|---|---|
| 2006 | 0.9170 (0.0649) |
| 2007 | 1.0400 (0.1692) |
| 2008 | 0.7960 (0.0803) |
| 2009 | 1.0230 (0.0895) |
| 2010 | 1.0760 (0.1678) |
| 2011 | 0.9750 (0.0580) |
| 2012 | 0.9720 (0.0377) |
| 2013 | 1.0190 (0.0915) |
| 2014 | 0.8730 (0.0723) |
| 2015 | 1.0970 (0.2469) |
| 2016 | 0.8680 (0.0580) |
| 2017 | 1.0360 (0.0762) |
| 2018 | 0.9320 (0.0840) |
| 2019 | 1.0580 (0.1566) |
| 2020 | 0.9470 (0.3161) |
| 2021 | 1.5850 (1.2094) |
| 2022 | 1.0050 (0.2651) |
| 2023 | 0.8250 (0.1142) |
| 2024 | 0.5120 (0.2459) |
