| Year | Value (SE) |
|---|---|
| 2002 | 0.8308 (0.0333) |
| 2003 | 0.8418 (0.0280) |
| 2004 | 0.7991 (0.0128) |
| 2006 | 0.9233 (0.0121) |
| 2008 | 0.9024 (0.0281) |
| 2009 | 0.9391 (0.0217) |
| 2010 | 0.8502 (0.0516) |
| 2011 | 0.9254 (0.0267) |
| 2013 | 0.9284 (0.0504) |
| 2014 | 0.8786 (0.0423) |
| 2016 | 0.9626 (0.0426) |
| 2019 | 0.9149 (0.0356) |
