| Year | Value (SE) |
|---|---|
| 2002 | 0.6106 (0.0793) |
| 2004 | 0.8491 (0.4896) |
| 2005 | 0.4712 (0.2109) |
| 2007 | 0.5815 (0.1211) |
| 2008 | 0.8405 (0.1534) |
| 2009 | 0.7133 (0.1253) |
| 2010 | 0.7399 (0.0934) |
| 2011 | 0.7208 (0.0396) |
| 2012 | 0.9467 (0.0459) |
| 2013 | 0.7573 (0.0760) |
| 2014 | 0.8543 (0.0769) |
| 2015 | 0.4648 (0.2318) |
