| Year | Value (SE) |
|---|---|
| 2000 | 0.8260 (0.0090) |
| 2002 | 0.8200 (0.0111) |
| 2003 | 0.7040 (0.0075) |
| 2004 | 0.8490 (0.0035) |
| 2005 | 0.8320 (0.0027) |
| 2006 | 0.8510 (0.0073) |
| 2007 | 0.8160 (0.0069) |
| 2008 | 0.7370 (0.0110) |
| 2009 | 0.6930 (0.0070) |
| 2010 | 0.8930 (0.0165) |
| 2011 | 0.7230 (0.0062) |
| 2012 | 0.7440 (0.0080) |
| 2013 | 0.7930 (0.0148) |
| 2014 | 0.8160 (0.0093) |
| 2015 | 0.7690 (0.0178) |
| 2016 | 0.7140 (0.0068) |
| 2017 | 0.6540 (0.0138) |
| 2020 | 0.8150 (0.0115) |
| 2021 | 0.7860 (0.0125) |
| 2022 | 0.8900 (0.0194) |
| 2023 | 0.8190 (0.0108) |
