| Year | Value (SE) |
|---|---|
| 2008 | 0.7806 (0.0681) |
| 2009 | 0.8317 (0.0495) |
| 2010 | 0.7898 (0.1696) |
| 2011 | 0.7638 (0.0237) |
| 2013 | 0.6898 (0.1149) |
| 2014 | 0.8078 (0.1268) |
| 2015 | 0.7605 (0.3218) |
| 2016 | 0.7789 (0.0821) |
| 2017 | 0.6797 (0.0581) |
| 2018 | 1.0967 (0.2172) |
| 2019 | 0.7953 (0.1445) |
| 2020 | 0.6222 (0.3273) |
| 2021 | 0.6081 (0.2362) |
| 2023 | 0.5880 (0.1868) |
| 2024 | 0.8071 (0.3879) |
