| Year | Value (SE) |
|---|---|
| 2003 | 0.8670 (0.0950) |
| 2004 | 0.9020 (0.1174) |
| 2005 | 0.8970 (0.0709) |
| 2006 | 0.9530 (0.1018) |
| 2008 | 1.3340 (0.2453) |
| 2009 | 1.0400 (0.1198) |
| 2010 | 1.2070 (0.2237) |
| 2011 | 1.0220 (0.1106) |
| 2013 | 1.1380 (0.1787) |
| 2014 | 1.2610 (0.2156) |
| 2015 | 0.9630 (0.4074) |
| 2019 | 1.0040 (0.2026) |
| 2020 | 2.0850 (1.2430) |
| 2023 | 1.9450 (0.5781) |
