| Year | Value (SE) |
|---|---|
| 2000 | 0.6750 (0.2910) |
| 2001 | 0.7630 (0.0628) |
| 2002 | 0.9170 (0.0839) |
| 2003 | 0.7630 (0.0706) |
| 2004 | 0.7190 (0.1364) |
| 2005 | 0.6500 (0.1168) |
| 2006 | 0.7300 (0.0912) |
| 2007 | 0.9200 (0.0577) |
| 2008 | 1.1140 (0.1734) |
| 2009 | 0.8680 (0.1215) |
| 2010 | 0.9960 (0.1364) |
| 2011 | 0.9710 (0.2099) |
| 2012 | 0.8260 (0.0868) |
| 2013 | 1.0760 (0.2178) |
| 2014 | 1.1130 (0.1651) |
| 2015 | 0.5770 (0.0979) |
| 2016 | 0.6040 (0.0620) |
| 2019 | 0.8030 (0.1268) |
| 2020 | 0.6730 (0.0940) |
| 2021 | 0.8960 (0.2537) |
| 2022 | 0.7880 (0.1922) |
| 2023 | 0.6970 (0.1144) |
