| Year | Value (SE) |
|---|---|
| 2002 | 0.5624 (0.0143) |
| 2007 | 0.7962 (0.0388) |
| 2008 | 0.7577 (0.0181) |
| 2009 | 0.8781 (0.0239) |
| 2010 | 0.9341 (0.0501) |
| 2011 | 0.8686 (0.0109) |
| 2012 | 0.8448 (0.0139) |
| 2013 | 0.8610 (0.0424) |
| 2014 | 0.7322 (0.0343) |
| 2015 | 0.6869 (0.0615) |
| 2018 | 0.7497 (0.0267) |
| 2019 | 0.5434 (0.0267) |
| 2020 | 0.6865 (0.1079) |
| 2021 | 0.5685 (0.1094) |
| 2022 | 0.6863 (0.0438) |
| 2023 | 0.6543 (0.0448) |
| 2024 | 0.6564 (0.0862) |
