| Year | Value (SE) |
|---|---|
| 2007 | 0.8336 (0.0687) |
| 2008 | 0.9255 (0.2394) |
| 2009 | 0.6601 (0.1099) |
| 2010 | 0.8055 (0.1343) |
| 2011 | 0.5932 (0.0940) |
| 2012 | 0.7577 (0.0655) |
| 2013 | 0.6448 (0.0748) |
| 2014 | 0.9235 (0.1003) |
| 2015 | 0.6021 (0.1072) |
| 2016 | 0.7239 (0.0586) |
| 2017 | 0.7375 (0.0789) |
| 2018 | 0.7405 (0.1281) |
| 2019 | 0.6467 (0.1001) |
| 2020 | 0.5887 (0.2021) |
| 2021 | 0.5612 (0.3946) |
| 2022 | 0.5506 (0.1981) |
| 2023 | 0.6748 (0.1416) |
| 2024 | 0.4161 (0.4054) |
