| Year | Value (SE) |
|---|---|
| 2001 | 0.4020 (0.1034) |
| 2002 | 0.8030 (0.1640) |
| 2003 | 1.3070 (0.5655) |
| 2004 | 0.6000 (0.2260) |
| 2005 | 0.6490 (0.3581) |
| 2007 | 1.0230 (0.3236) |
| 2008 | 1.0340 (0.2277) |
| 2009 | 0.9930 (0.3191) |
| 2010 | 1.0910 (0.2866) |
| 2011 | 0.6340 (0.2143) |
| 2012 | 0.7770 (0.1997) |
| 2013 | 1.2570 (0.4780) |
| 2014 | 0.5670 (0.1300) |
| 2015 | 0.2840 (0.3927) |
| 2016 | 0.6070 (0.2195) |
| 2017 | 1.0380 (0.5364) |
| 2018 | 0.6510 (0.2156) |
| 2020 | 0.7080 (0.2652) |
| 2021 | 0.0970 (0.0978) |
| 2022 | 0.6890 (0.2015) |
| 2023 | 0.9280 (0.2867) |
