| Year | Value (SE) |
|---|---|
| 2003 | 0.7183 (0.0467) |
| 2007 | 0.6760 (0.1404) |
| 2008 | 0.7393 (0.0349) |
| 2009 | 0.8883 (0.0471) |
| 2010 | 0.9182 (0.1008) |
| 2011 | 0.9032 (0.0356) |
| 2012 | 0.9044 (0.0478) |
| 2013 | 0.6954 (0.0786) |
| 2014 | 0.6396 (0.0781) |
| 2015 | 0.7757 (0.1743) |
| 2018 | 0.7709 (0.0517) |
| 2019 | 0.7742 (0.0899) |
| 2020 | 0.8078 (0.2798) |
| 2021 | 0.4584 (0.1797) |
| 2022 | 0.6126 (0.1211) |
| 2023 | 0.6218 (0.1240) |
