| Year | Value (SE) |
|---|---|
| 2000 | 0.6990 (0.0194) |
| 2001 | 0.7120 (0.0149) |
| 2002 | 0.9220 (0.0228) |
| 2003 | 0.9100 (0.0226) |
| 2004 | 0.8860 (0.0071) |
| 2005 | 0.9400 (0.0064) |
| 2006 | 0.9700 (0.0182) |
| 2007 | 0.8580 (0.0358) |
| 2008 | 0.9140 (0.0271) |
| 2009 | 0.9610 (0.0200) |
| 2010 | 0.9860 (0.0503) |
| 2011 | 0.9580 (0.0305) |
| 2013 | 0.9320 (0.0478) |
| 2014 | 0.9760 (0.0506) |
| 2015 | 1.1840 (0.1031) |
| 2016 | 0.9830 (0.0334) |
| 2019 | 0.9100 (0.0364) |
| 2022 | 0.8950 (0.1462) |
| 2023 | 0.7340 (0.0769) |
