| Year | Value (SE) |
|---|---|
| 2008 | 0.7133 (0.0910) |
| 2009 | 0.8572 (0.0424) |
| 2010 | 0.6594 (0.1792) |
| 2011 | 0.7432 (0.0260) |
| 2012 | 0.7558 (0.0269) |
| 2013 | 0.9339 (0.0765) |
| 2014 | 0.8849 (0.0436) |
| 2015 | 0.7120 (0.1274) |
| 2016 | 0.6642 (0.0490) |
| 2017 | 0.7564 (0.0729) |
| 2018 | 0.5419 (0.0797) |
| 2019 | 0.5719 (0.0959) |
| 2020 | 0.6351 (0.2253) |
| 2021 | 0.8073 (0.9580) |
| 2022 | 0.8359 (0.3093) |
