| Year | Value (SE) |
|---|---|
| 2000 | 0.8020 (0.0829) |
| 2001 | 0.6790 (0.0228) |
| 2002 | 0.8170 (0.0284) |
| 2003 | 1.0000 (0.0547) |
| 2004 | 0.8660 (0.0485) |
| 2005 | 0.9750 (0.0615) |
| 2006 | 0.8280 (0.0395) |
| 2007 | 0.8240 (0.0488) |
| 2008 | 0.9620 (0.1141) |
| 2009 | 0.7160 (0.0554) |
| 2010 | 0.8430 (0.1139) |
| 2011 | 0.9730 (0.2282) |
| 2012 | 1.0560 (0.0775) |
| 2013 | 1.0330 (0.1055) |
| 2014 | 0.8200 (0.1003) |
| 2015 | 0.7950 (0.2585) |
| 2016 | 0.7950 (0.0928) |
| 2018 | 0.8300 (0.1259) |
| 2019 | 0.8220 (0.1206) |
| 2020 | 1.0260 (0.2669) |
| 2021 | 0.5860 (0.3997) |
| 2022 | 0.8330 (0.4273) |
| 2023 | 0.6360 (0.1422) |
