| Year | Value (SE) |
|---|---|
| 2000 | 0.5999 (0.0293) |
| 2001 | 0.5348 (0.0146) |
| 2002 | 0.7041 (0.0419) |
| 2003 | 0.7770 (0.0360) |
| 2005 | 0.7603 (0.0099) |
| 2007 | 0.8367 (0.0439) |
| 2008 | 0.8091 (0.0298) |
| 2010 | 0.7703 (0.0480) |
| 2012 | 0.9159 (0.0409) |
| 2013 | 0.8761 (0.0641) |
| 2015 | 0.9152 (0.1202) |
| 2019 | 0.8215 (0.0527) |
