| Year | Value (SE) |
|---|---|
| 2009 | 0.8630 (0.1018) |
| 2010 | 0.9630 (0.1085) |
| 2011 | 0.8490 (0.0579) |
| 2012 | 0.9580 (0.0629) |
| 2013 | 1.0330 (0.1074) |
| 2014 | 1.0090 (0.2024) |
| 2015 | 1.3150 (0.3410) |
| 2016 | 0.8990 (0.0669) |
| 2017 | 0.8740 (0.0928) |
| 2018 | 0.7580 (0.1200) |
| 2019 | 0.8840 (0.1312) |
| 2020 | 1.2430 (0.2417) |
| 2022 | 0.4460 (0.2189) |
| 2023 | 0.9140 (0.1801) |
