| Year | Value (SE) |
|---|---|
| 2006 | 0.7957 (0.0881) |
| 2007 | 0.8516 (0.1488) |
| 2008 | 0.6165 (0.1017) |
| 2009 | 0.7913 (0.0845) |
| 2010 | 0.9068 (0.1515) |
| 2011 | 0.8828 (0.0895) |
| 2012 | 0.8823 (0.0510) |
| 2013 | 0.9013 (0.0962) |
| 2014 | 0.9538 (0.1055) |
| 2015 | 0.9102 (0.2163) |
| 2016 | 0.6937 (0.0584) |
| 2017 | 0.8366 (0.0991) |
| 2018 | 0.7952 (0.0985) |
| 2019 | 0.9521 (0.2483) |
| 2020 | 0.5914 (0.2117) |
| 2021 | 0.7778 (0.6012) |
| 2022 | 0.9162 (0.3942) |
| 2023 | 0.5148 (0.1025) |
| 2024 | 0.5933 (0.3038) |
