| Year | Value (SE) |
|---|---|
| 2008 | 0.9440 (0.0562) |
| 2009 | 0.9400 (0.0531) |
| 2013 | 0.9560 (0.1006) |
| 2014 | 1.1300 (0.1254) |
| 2015 | 1.0280 (0.2741) |
| 2016 | 0.8250 (0.1227) |
| 2017 | 0.9410 (0.0556) |
| 2018 | 0.7250 (0.0610) |
| 2019 | 0.8200 (0.0876) |
| 2020 | 0.9080 (0.4120) |
| 2021 | 3.1720 (3.1930) |
| 2022 | 1.0910 (0.4652) |
| 2023 | 0.7340 (0.0945) |
