| Year | Value (SE) |
|---|---|
| 2006 | 0.7410 (0.0501) |
| 2007 | 0.9930 (0.1890) |
| 2008 | 0.7630 (0.0847) |
| 2009 | 0.8660 (0.0778) |
| 2010 | 0.8320 (0.1293) |
| 2011 | 0.6340 (0.0501) |
| 2012 | 1.4930 (0.2933) |
| 2013 | 0.8230 (0.5348) |
| 2014 | 0.6850 (0.2026) |
| 2016 | 0.9760 (0.1485) |
| 2017 | 1.0180 (0.2244) |
| 2018 | 0.8260 (0.1859) |
| 2019 | 0.8960 (0.2412) |
| 2020 | 0.6970 (0.6508) |
