| Year | Value (SE) |
|---|---|
| 2008 | 0.7750 (0.0538) |
| 2009 | 0.7962 (0.0161) |
| 2010 | 0.7301 (0.0286) |
| 2011 | 0.6920 (0.0162) |
| 2012 | 0.6755 (0.0117) |
| 2013 | 0.6997 (0.0197) |
| 2014 | 0.7625 (0.0197) |
| 2015 | 0.9275 (0.0647) |
| 2016 | 0.7996 (0.0196) |
| 2017 | 0.8208 (0.0269) |
| 2018 | 0.8264 (0.0194) |
| 2019 | 0.7081 (0.0196) |
| 2020 | 0.7611 (0.0560) |
| 2021 | 0.7027 (0.0932) |
| 2022 | 0.7986 (0.0860) |
| 2023 | 0.7007 (0.0369) |
| 2024 | 0.6475 (0.0845) |
