| Year | Value (SE) |
|---|---|
| 2008 | 0.6121 (0.1379) |
| 2009 | 0.6122 (0.0792) |
| 2010 | 0.7311 (0.1341) |
| 2011 | 0.6821 (0.0595) |
| 2012 | 0.7247 (0.0682) |
| 2013 | 0.7740 (0.1149) |
| 2014 | 0.6221 (0.0981) |
| 2015 | 0.5934 (0.1385) |
| 2016 | 0.6365 (0.0739) |
| 2018 | 0.6360 (0.1659) |
| 2019 | 0.4183 (0.0716) |
| 2020 | 0.9075 (0.5428) |
| 2022 | 0.5327 (0.2383) |
| 2023 | 0.7890 (0.2704) |
