| Year | Value (SE) |
|---|---|
| 2008 | 1.2065 (0.3458) |
| 2009 | 0.9744 (0.2178) |
| 2010 | 0.9004 (0.2023) |
| 2011 | 1.2999 (0.1802) |
| 2012 | 1.0170 (0.1442) |
| 2013 | 0.9502 (0.2037) |
| 2014 | 0.7263 (0.1527) |
| 2015 | 0.7610 (0.1816) |
| 2016 | 0.5518 (0.0853) |
| 2018 | 1.7142 (0.9253) |
| 2019 | 0.9679 (0.2953) |
| 2020 | 0.8881 (0.5444) |
| 2022 | 0.7954 (0.4081) |
| 2023 | 0.8419 (0.3110) |
