| Year | Value (SE) |
|---|---|
| 2007 | 0.7952 (0.0762) |
| 2008 | 0.8080 (0.2127) |
| 2009 | 0.7275 (0.1236) |
| 2010 | 0.7362 (0.1314) |
| 2011 | 0.6383 (0.1018) |
| 2012 | 0.7190 (0.0629) |
| 2013 | 0.6938 (0.0827) |
| 2014 | 0.8506 (0.0947) |
| 2015 | 0.5088 (0.0999) |
| 2016 | 0.5864 (0.0496) |
| 2017 | 0.6947 (0.0760) |
| 2018 | 0.5976 (0.1068) |
| 2019 | 0.6726 (0.1100) |
| 2020 | 0.6611 (0.2515) |
| 2021 | 0.5904 (0.5236) |
| 2022 | 0.8039 (0.3014) |
| 2023 | 0.6808 (0.1473) |
| 2024 | 0.3761 (0.3872) |
