| Year | Value (SE) |
|---|---|
| 2008 | 0.8030 (0.0278) |
| 2009 | 0.7400 (0.0145) |
| 2013 | 0.4930 (0.0188) |
| 2014 | 0.6660 (0.0195) |
| 2015 | 0.7690 (0.1035) |
| 2016 | 0.6810 (0.0206) |
| 2017 | 0.7590 (0.0181) |
| 2018 | 0.6800 (0.0145) |
| 2019 | 0.4420 (0.0173) |
| 2020 | 0.5090 (0.0248) |
| 2021 | 0.6140 (0.0109) |
| 2022 | 0.7140 (0.0283) |
| 2023 | 0.6640 (0.0118) |
