| Year | Value (SE) |
|---|---|
| 2008 | 0.7504 (0.0248) |
| 2009 | 0.9627 (0.0212) |
| 2010 | 0.8271 (0.0836) |
| 2011 | 0.7719 (0.0079) |
| 2013 | 0.6166 (0.0351) |
| 2014 | 0.8030 (0.0463) |
| 2015 | 0.8434 (0.1787) |
| 2016 | 0.8536 (0.0374) |
| 2017 | 0.8157 (0.0227) |
| 2018 | 0.8466 (0.0389) |
| 2019 | 0.8593 (0.0480) |
| 2020 | 0.7735 (0.1181) |
| 2021 | 0.6971 (0.1006) |
| 2023 | 0.8581 (0.0967) |
| 2024 | 0.7257 (0.1814) |
