| Year | Value (SE) |
|---|---|
| 2006 | 0.9320 (0.0481) |
| 2007 | 0.9390 (0.0982) |
| 2008 | 0.8110 (0.0756) |
| 2009 | 1.0510 (0.0514) |
| 2010 | 0.9620 (0.0659) |
| 2011 | 1.0360 (0.0426) |
| 2012 | 0.8580 (0.0222) |
| 2013 | 1.0670 (0.0602) |
| 2014 | 1.0070 (0.0498) |
| 2015 | 1.0490 (0.1124) |
| 2016 | 1.0220 (0.0436) |
| 2017 | 0.8730 (0.0426) |
| 2018 | 1.0380 (0.0562) |
| 2019 | 0.8840 (0.0791) |
| 2020 | 0.7700 (0.1531) |
| 2021 | 0.8520 (0.3150) |
| 2022 | 0.7340 (0.1215) |
| 2023 | 1.0230 (0.0820) |
| 2024 | 0.7920 (0.1590) |
