| Year | Value (SE) |
|---|---|
| 2001 | 0.6690 (0.1978) |
| 2006 | 0.9240 (0.0539) |
| 2007 | 1.0380 (0.1007) |
| 2008 | 0.8000 (0.0550) |
| 2009 | 0.7480 (0.0684) |
| 2010 | 0.8380 (0.0536) |
| 2011 | 0.8180 (0.0842) |
| 2012 | 0.9740 (0.0792) |
| 2013 | 0.8650 (0.1709) |
| 2014 | 0.7070 (0.1887) |
| 2015 | 0.5050 (0.3082) |
| 2016 | 0.7980 (0.2473) |
| 2018 | 1.0210 (0.1236) |
| 2020 | 0.8320 (0.1956) |
| 2021 | 0.7640 (0.2038) |
| 2022 | 1.2350 (0.3580) |
| 2023 | 0.9220 (0.2173) |
| 2024 | 0.9320 (0.2671) |
