| Year | Value (SE) |
|---|---|
| 2008 | 0.7900 (0.1236) |
| 2009 | 0.9140 (0.1065) |
| 2011 | 0.8420 (0.0767) |
| 2012 | 1.1740 (0.1954) |
| 2013 | 0.8550 (0.1324) |
| 2014 | 0.8380 (0.1370) |
| 2015 | 1.1560 (0.4970) |
| 2016 | 0.7080 (0.0872) |
| 2018 | 0.7920 (0.1523) |
| 2019 | 1.0100 (0.1135) |
| 2020 | 1.0730 (0.1825) |
| 2021 | 0.7310 (0.2346) |
| 2022 | 1.5310 (0.5620) |
| 2023 | 0.5550 (0.2272) |
