| Year | Value (SE) |
|---|---|
| 2002 | 0.6400 (0.0780) |
| 2004 | 0.9760 (0.5438) |
| 2005 | 0.8400 (0.3346) |
| 2007 | 0.8960 (0.1573) |
| 2008 | 0.7620 (0.1348) |
| 2009 | 0.6580 (0.1097) |
| 2010 | 0.7550 (0.0885) |
| 2011 | 0.7860 (0.0400) |
| 2012 | 0.9760 (0.0460) |
| 2013 | 0.7650 (0.0729) |
| 2014 | 0.8700 (0.0643) |
| 2015 | 0.8270 (0.3137) |
