| Year | Value (SE) |
|---|---|
| 2007 | 0.6600 (0.0976) |
| 2009 | 0.7190 (0.1462) |
| 2010 | 0.7426 (0.1260) |
| 2011 | 0.8479 (0.1505) |
| 2012 | 0.5979 (0.0620) |
| 2013 | 0.5928 (0.1063) |
| 2014 | 0.6243 (0.0841) |
| 2015 | 0.4236 (0.2037) |
| 2016 | 0.5934 (0.0805) |
| 2018 | 0.7515 (0.1842) |
| 2019 | 0.5323 (0.1198) |
| 2020 | 0.9136 (0.3996) |
| 2021 | 0.6916 (0.7954) |
| 2022 | 0.6927 (0.9088) |
| 2023 | 0.5640 (0.2098) |
