| Year | Value (SE) |
|---|---|
| 2004 | 1.5280 (0.5160) |
| 2005 | 0.6710 (0.1974) |
| 2006 | 1.0480 (0.2074) |
| 2007 | 0.6190 (0.1514) |
| 2008 | 0.8960 (0.1009) |
| 2009 | 0.7930 (0.1620) |
| 2010 | 1.2430 (0.1866) |
| 2011 | 1.8270 (0.6728) |
| 2012 | 0.7430 (0.2359) |
| 2013 | 1.7170 (1.2135) |
| 2014 | 1.0550 (0.3095) |
| 2015 | 1.2760 (0.6920) |
