| Year | Value (SE) |
|---|---|
| 2008 | 0.5890 (0.0686) |
| 2009 | 0.7588 (0.0285) |
| 2010 | 0.8308 (0.0700) |
| 2011 | 0.6574 (0.0214) |
| 2012 | 0.6255 (0.0198) |
| 2013 | 0.6934 (0.0377) |
| 2014 | 0.7694 (0.0427) |
| 2015 | 0.9163 (0.1297) |
| 2016 | 0.6549 (0.0266) |
| 2017 | 0.6485 (0.0298) |
| 2018 | 0.6686 (0.0286) |
| 2019 | 0.6748 (0.0286) |
| 2020 | 0.9209 (0.1515) |
| 2021 | 0.6887 (0.1772) |
| 2022 | 0.5974 (0.0950) |
| 2023 | 0.5655 (0.0453) |
| 2024 | 0.6242 (0.1979) |
