| Year | Value (SE) |
|---|---|
| 2008 | 0.8357 (0.2309) |
| 2009 | 0.7200 (0.1098) |
| 2010 | 0.7626 (0.1063) |
| 2011 | 0.9578 (0.1429) |
| 2012 | 0.7555 (0.1138) |
| 2013 | 0.7777 (0.1722) |
| 2014 | 1.1331 (0.2424) |
| 2015 | 0.5067 (0.1506) |
| 2016 | 0.7955 (0.0804) |
| 2017 | 0.8311 (0.1314) |
| 2019 | 0.8350 (0.3497) |
| 2020 | 1.5612 (0.6162) |
| 2021 | 0.6178 (0.6389) |
