| Year | Value (SE) |
|---|---|
| 2006 | 0.5240 (0.0166) |
| 2007 | 0.7430 (0.0330) |
| 2008 | 0.6560 (0.0458) |
| 2009 | 0.3600 (0.0092) |
| 2010 | 0.6970 (0.0294) |
| 2011 | 0.3200 (0.0078) |
| 2012 | 0.6530 (0.0119) |
| 2013 | 0.5840 (0.0188) |
| 2014 | 0.4490 (0.0114) |
| 2015 | 0.4340 (0.0170) |
| 2016 | 0.6010 (0.0105) |
| 2017 | 0.5090 (0.0150) |
| 2018 | 0.6400 (0.0174) |
| 2019 | 0.2650 (0.0134) |
| 2020 | 0.6250 (0.0245) |
| 2021 | 0.8220 (0.0209) |
| 2022 | 0.8900 (0.0236) |
| 2023 | 0.8160 (0.0146) |
| 2024 | 0.5640 (0.0330) |
