| Year | Value (SE) |
|---|---|
| 2008 | 0.8284 (0.1522) |
| 2009 | 0.8669 (0.0868) |
| 2010 | 0.6669 (0.1933) |
| 2011 | 0.6097 (0.0478) |
| 2012 | 0.8810 (0.0567) |
| 2013 | 0.7273 (0.0754) |
| 2014 | 0.8299 (0.0645) |
| 2015 | 1.1842 (0.2866) |
| 2016 | 0.6487 (0.0749) |
| 2017 | 0.8714 (0.1010) |
| 2018 | 0.5793 (0.1152) |
| 2019 | 0.6745 (0.1607) |
| 2020 | 0.3593 (0.1270) |
| 2021 | 0.5099 (0.5265) |
| 2022 | 0.6448 (0.2683) |
