| Year | Value (SE) |
|---|---|
| 2007 | 0.8412 (0.0726) |
| 2008 | 0.8023 (0.1336) |
| 2009 | 0.8365 (0.0707) |
| 2010 | 0.7422 (0.1092) |
| 2011 | 0.7136 (0.0552) |
| 2012 | 0.8414 (0.0495) |
| 2013 | 1.0302 (0.0902) |
| 2014 | 0.9423 (0.0625) |
| 2015 | 0.7303 (0.1227) |
| 2016 | 0.7016 (0.0337) |
| 2017 | 0.8016 (0.0634) |
| 2018 | 0.7146 (0.0826) |
| 2019 | 0.6651 (0.0897) |
| 2020 | 0.7164 (0.2566) |
| 2021 | 0.7339 (0.6354) |
| 2022 | 0.4840 (0.1563) |
| 2023 | 0.6847 (0.1197) |
| 2024 | 0.5624 (0.5669) |
