| Year | Value (SE) |
|---|---|
| 2000 | 0.6880 (0.0333) |
| 2001 | 0.6770 (0.0176) |
| 2002 | 0.8890 (0.0522) |
| 2003 | 0.8720 (0.0400) |
| 2005 | 0.9160 (0.0092) |
| 2007 | 0.8770 (0.0460) |
| 2008 | 0.8980 (0.0327) |
| 2010 | 0.9020 (0.0559) |
| 2012 | 0.9880 (0.0438) |
| 2013 | 0.7900 (0.0581) |
| 2015 | 1.0780 (0.1415) |
| 2019 | 0.8920 (0.0566) |
