| Year | Value (SE) |
|---|---|
| 2000 | 0.8830 (0.0373) |
| 2001 | 0.9500 (0.0089) |
| 2002 | 0.9400 (0.0186) |
| 2003 | 0.9120 (0.0258) |
| 2004 | 0.9830 (0.0100) |
| 2005 | 0.9350 (0.0102) |
| 2006 | 0.8880 (0.0180) |
| 2007 | 0.9430 (0.0339) |
| 2008 | 0.9430 (0.0372) |
| 2009 | 0.9510 (0.0313) |
| 2010 | 0.9530 (0.0675) |
| 2011 | 0.9900 (0.0692) |
| 2012 | 0.8590 (0.0297) |
| 2013 | 0.9810 (0.0365) |
| 2014 | 1.0750 (0.0531) |
| 2015 | 0.9700 (0.1551) |
| 2016 | 0.9630 (0.0456) |
| 2018 | 1.0600 (0.0434) |
| 2019 | 0.9380 (0.0576) |
| 2020 | 0.8770 (0.1110) |
| 2021 | 1.0900 (0.4159) |
| 2022 | 0.7500 (0.0989) |
| 2023 | 1.0540 (0.1041) |
