| Year | Value (SE) |
|---|---|
| 2006 | 0.8537 (0.0898) |
| 2007 | 0.9069 (0.1547) |
| 2008 | 0.7602 (0.1114) |
| 2009 | 0.7529 (0.0788) |
| 2010 | 0.9426 (0.1518) |
| 2011 | 0.8521 (0.0844) |
| 2012 | 1.0284 (0.0565) |
| 2013 | 0.8448 (0.0857) |
| 2014 | 0.9472 (0.1025) |
| 2015 | 0.8677 (0.2047) |
| 2016 | 0.6788 (0.0568) |
| 2017 | 0.9583 (0.1102) |
| 2018 | 0.7661 (0.0928) |
| 2019 | 1.0770 (0.2765) |
| 2020 | 0.7680 (0.2743) |
| 2021 | 0.9130 (0.7057) |
| 2022 | 1.2482 (0.5373) |
| 2023 | 0.5032 (0.1003) |
| 2024 | 0.7491 (0.3818) |
