| Year | Value (SE) |
|---|---|
| 2000 | 0.8720 (0.0180) |
| 2001 | 0.7900 (0.0081) |
| 2002 | 0.7920 (0.0323) |
| 2003 | 0.8910 (0.0267) |
| 2005 | 0.8300 (0.0081) |
| 2007 | 0.9540 (0.0368) |
| 2008 | 0.9010 (0.0213) |
| 2010 | 0.8540 (0.0341) |
| 2012 | 0.9270 (0.0228) |
| 2013 | 1.1090 (0.0628) |
| 2015 | 0.8490 (0.0739) |
| 2019 | 0.9210 (0.0391) |
