| Year | Value (SE) |
|---|---|
| 2000 | 1.1590 (0.3645) |
| 2001 | 0.8940 (0.1042) |
| 2002 | 1.2680 (0.1210) |
| 2003 | 0.8950 (0.0662) |
| 2004 | 1.0610 (0.1471) |
| 2005 | 0.7130 (0.1081) |
| 2006 | 0.8830 (0.0820) |
| 2007 | 0.8100 (0.0511) |
| 2008 | 0.9060 (0.1869) |
| 2009 | 0.7090 (0.1079) |
| 2010 | 1.3100 (0.3063) |
| 2011 | 0.3660 (0.1145) |
| 2012 | 0.6210 (0.0647) |
| 2013 | 0.6580 (0.1076) |
| 2014 | 0.9140 (0.1915) |
| 2015 | 0.5250 (0.1878) |
| 2016 | 0.8080 (0.1823) |
| 2018 | 0.8650 (0.1970) |
| 2019 | 1.0900 (0.2249) |
| 2020 | 0.7400 (0.1908) |
| 2021 | 0.6610 (0.2656) |
| 2022 | 0.8780 (0.5349) |
| 2023 | 1.2380 (0.3608) |
