| Year | Value (SE) |
|---|---|
| 2008 | 1.4600 (0.2346) |
| 2009 | 0.9640 (0.0845) |
| 2010 | 0.9330 (0.0796) |
| 2011 | 1.1370 (0.1177) |
| 2012 | 0.9400 (0.0848) |
| 2013 | 0.8990 (0.0884) |
| 2014 | 0.8440 (0.0932) |
| 2015 | 0.6830 (0.0833) |
| 2016 | 0.8920 (0.0748) |
| 2017 | 0.8560 (0.0865) |
| 2018 | 0.9610 (0.1193) |
| 2019 | 1.3100 (0.1547) |
| 2020 | 1.1250 (0.2023) |
| 2021 | 0.9500 (0.2267) |
| 2022 | 0.9920 (0.3246) |
| 2023 | 1.0570 (0.1772) |
| 2024 | 0.5280 (0.2050) |
