| Year | Value (SE) |
|---|---|
| 2002 | 0.4259 (0.0461) |
| 2003 | 0.5435 (0.0571) |
| 2004 | 0.3160 (0.0702) |
| 2006 | 0.6666 (0.0330) |
| 2008 | 0.6930 (0.0649) |
| 2009 | 0.7626 (0.0542) |
| 2010 | 0.7015 (0.1335) |
| 2011 | 0.8062 (0.0781) |
| 2013 | 0.6127 (0.1046) |
| 2014 | 0.5873 (0.0980) |
| 2016 | 0.6487 (0.0656) |
| 2019 | 0.7749 (0.1268) |
