| Year | Value (SE) |
|---|---|
| 2002 | 0.4524 (0.0664) |
| 2004 | 0.8101 (0.4626) |
| 2005 | 0.3685 (0.1603) |
| 2007 | 0.6187 (0.1346) |
| 2008 | 0.7749 (0.1487) |
| 2009 | 0.6705 (0.1220) |
| 2010 | 0.6844 (0.0894) |
| 2011 | 0.6516 (0.0364) |
| 2012 | 0.7526 (0.0376) |
| 2013 | 0.6937 (0.0699) |
| 2014 | 0.7903 (0.0760) |
| 2015 | 1.0262 (0.5828) |
