| Year | Value (SE) |
|---|---|
| 2000 | 0.7060 (0.0575) |
| 2001 | 0.3650 (0.0497) |
| 2002 | 0.5330 (0.0337) |
| 2003 | 0.6930 (0.0567) |
| 2004 | 0.5270 (0.0747) |
| 2005 | 0.8670 (0.0771) |
| 2006 | 0.7620 (0.0523) |
| 2007 | 0.9730 (0.1431) |
| 2008 | 0.7840 (0.0679) |
| 2009 | 0.8440 (0.0491) |
| 2010 | 0.9270 (0.1063) |
| 2011 | 0.7600 (0.0788) |
| 2013 | 0.6850 (0.0900) |
| 2014 | 0.6090 (0.0886) |
| 2015 | 0.7640 (0.1397) |
| 2016 | 0.8870 (0.0750) |
| 2019 | 0.5870 (0.0760) |
| 2022 | 1.7290 (1.2749) |
| 2023 | 0.6690 (0.2567) |
