| Year | Value (SE) |
|---|---|
| 2007 | 0.8681 (0.0710) |
| 2008 | 0.8145 (0.1327) |
| 2009 | 0.8518 (0.0706) |
| 2010 | 0.7422 (0.1045) |
| 2011 | 0.7457 (0.0568) |
| 2012 | 0.9338 (0.0531) |
| 2013 | 1.0545 (0.0897) |
| 2014 | 0.8823 (0.0579) |
| 2015 | 0.6633 (0.1064) |
| 2016 | 0.7023 (0.0339) |
| 2017 | 0.8619 (0.0668) |
| 2018 | 0.6722 (0.0761) |
| 2019 | 0.7415 (0.0954) |
| 2020 | 0.6671 (0.2388) |
| 2021 | 0.5881 (0.5094) |
| 2022 | 0.8161 (0.2636) |
| 2023 | 0.7658 (0.1342) |
| 2024 | 0.5062 (0.5103) |
