| Year | Value (SE) |
|---|---|
| 2007 | 0.9100 (0.0598) |
| 2008 | 0.9330 (0.1450) |
| 2009 | 0.7730 (0.0585) |
| 2010 | 0.8120 (0.1020) |
| 2011 | 0.6930 (0.0514) |
| 2012 | 0.9840 (0.0543) |
| 2013 | 0.9800 (0.0791) |
| 2014 | 0.9580 (0.0583) |
| 2015 | 0.7850 (0.1078) |
| 2016 | 0.8670 (0.0361) |
| 2017 | 0.9150 (0.0677) |
| 2018 | 0.8330 (0.0865) |
| 2019 | 0.7130 (0.0836) |
| 2020 | 0.5940 (0.1890) |
| 2021 | 0.5590 (0.3783) |
| 2022 | 0.5590 (0.1706) |
| 2023 | 0.7590 (0.1269) |
| 2024 | 0.5600 (0.5329) |
