| Year | Value (SE) |
|---|---|
| 2002 | 0.8947 (0.0587) |
| 2003 | 0.7424 (0.0416) |
| 2004 | 0.6409 (0.0418) |
| 2006 | 0.8189 (0.0184) |
| 2008 | 0.7743 (0.0510) |
| 2009 | 0.8940 (0.0367) |
| 2010 | 1.2990 (0.2217) |
| 2011 | 0.8948 (0.0440) |
| 2013 | 0.9340 (0.0984) |
| 2014 | 0.9428 (0.0927) |
| 2016 | 0.7509 (0.0502) |
| 2019 | 0.8244 (0.0491) |
