| Year | Value (SE) |
|---|---|
| 2008 | 0.5893 (0.0528) |
| 2009 | 0.7322 (0.0378) |
| 2010 | 0.7572 (0.1081) |
| 2011 | 0.6935 (0.0179) |
| 2012 | 0.6027 (0.0191) |
| 2013 | 0.5922 (0.0490) |
| 2014 | 0.5979 (0.0266) |
| 2015 | 0.7981 (0.1444) |
| 2016 | 0.6378 (0.0236) |
| 2017 | 0.6369 (0.0360) |
| 2018 | 0.5675 (0.0358) |
| 2019 | 0.4366 (0.0278) |
| 2020 | 0.4343 (0.1552) |
| 2021 | 0.9243 (0.6674) |
| 2022 | 0.4036 (0.1068) |
| 2023 | 0.4914 (0.0908) |
