| Year | Value (SE) |
|---|---|
| 2006 | 1.1360 (0.0853) |
| 2007 | 0.9590 (0.1160) |
| 2008 | 1.1500 (0.1251) |
| 2009 | 0.8720 (0.1029) |
| 2010 | 0.8650 (0.0936) |
| 2011 | 1.0480 (0.1414) |
| 2012 | 0.8070 (0.1465) |
| 2013 | 0.7140 (0.1674) |
| 2014 | 1.1960 (0.2624) |
| 2016 | 0.9040 (0.1250) |
| 2017 | 0.7370 (0.1741) |
| 2018 | 0.9240 (0.1661) |
| 2019 | 0.8030 (0.1979) |
| 2020 | 1.0420 (0.2517) |
