| Year | Value (SE) |
|---|---|
| 2007 | 0.7706 (0.0768) |
| 2008 | 0.7959 (0.2113) |
| 2009 | 0.7144 (0.1219) |
| 2010 | 0.7362 (0.1351) |
| 2011 | 0.6108 (0.0977) |
| 2012 | 0.6479 (0.0575) |
| 2013 | 0.6779 (0.0820) |
| 2014 | 0.9084 (0.1016) |
| 2015 | 0.5602 (0.1135) |
| 2016 | 0.5858 (0.0494) |
| 2017 | 0.6461 (0.0714) |
| 2018 | 0.6353 (0.1145) |
| 2019 | 0.6033 (0.1016) |
| 2020 | 0.7100 (0.2703) |
| 2021 | 0.7368 (0.6532) |
| 2022 | 0.4767 (0.1788) |
| 2023 | 0.6087 (0.1315) |
| 2024 | 0.4179 (0.4302) |
