| Year | Value (SE) |
|---|---|
| 2011 | 0.6926 (0.0504) |
| 2012 | 0.6682 (0.0619) |
| 2013 | 0.5833 (0.0587) |
| 2014 | 0.6270 (0.0770) |
| 2015 | 0.4244 (0.0927) |
| 2016 | 0.6062 (0.0798) |
| 2017 | 0.6996 (0.1157) |
| 2018 | 0.5799 (0.0525) |
| 2019 | 0.4092 (0.0639) |
| 2020 | 0.5167 (0.1680) |
| 2021 | 0.2670 (0.1863) |
| 2022 | 0.4039 (0.0945) |
| 2023 | 0.4587 (0.0744) |
