| Year | Value (SE) |
|---|---|
| 2008 | 0.6929 (0.0531) |
| 2009 | 0.8343 (0.0310) |
| 2010 | 0.7964 (0.0601) |
| 2011 | 0.8610 (0.0261) |
| 2012 | 0.7645 (0.0180) |
| 2013 | 0.7406 (0.0394) |
| 2014 | 0.7938 (0.0379) |
| 2015 | 0.7032 (0.0960) |
| 2016 | 0.8149 (0.0410) |
| 2018 | 0.7816 (0.0458) |
| 2019 | 0.7458 (0.0383) |
| 2020 | 0.7571 (0.1544) |
| 2022 | 0.6625 (0.1106) |
| 2023 | 0.7269 (0.0603) |
