| Year | Value (SE) |
|---|---|
| 2002 | 0.9725 (0.0636) |
| 2003 | 0.8573 (0.0476) |
| 2004 | 0.6921 (0.0449) |
| 2006 | 0.8666 (0.0192) |
| 2008 | 0.8237 (0.0542) |
| 2009 | 0.9644 (0.0394) |
| 2010 | 1.2575 (0.2147) |
| 2011 | 0.9622 (0.0471) |
| 2013 | 1.0412 (0.1098) |
| 2014 | 1.0236 (0.1007) |
| 2016 | 0.7862 (0.0525) |
| 2019 | 0.8893 (0.0529) |
