| Year | Value (SE) |
|---|---|
| 2008 | 0.7504 (0.1375) |
| 2009 | 0.8161 (0.0932) |
| 2010 | 0.7837 (0.1312) |
| 2011 | 0.8419 (0.0681) |
| 2012 | 0.7575 (0.0585) |
| 2013 | 0.7093 (0.0916) |
| 2014 | 0.6494 (0.0587) |
| 2015 | 0.6630 (0.1592) |
| 2016 | 0.6674 (0.0499) |
| 2017 | 0.6704 (0.0735) |
| 2018 | 0.6975 (0.0840) |
| 2019 | 1.0162 (0.1620) |
| 2020 | 0.7872 (0.3269) |
| 2021 | 0.8127 (0.6110) |
| 2022 | 1.6098 (0.9097) |
| 2023 | 0.4506 (0.1219) |
