| Year | Value (SE) |
|---|---|
| 2008 | 1.2660 (0.3197) |
| 2009 | 1.2770 (0.2661) |
| 2010 | 0.9790 (0.1747) |
| 2011 | 1.4160 (0.1896) |
| 2012 | 1.0020 (0.1365) |
| 2013 | 1.1100 (0.2169) |
| 2014 | 1.0650 (0.1956) |
| 2015 | 0.8900 (0.1450) |
| 2016 | 0.6640 (0.0908) |
| 2018 | 0.8060 (0.2305) |
| 2019 | 1.6930 (0.3700) |
| 2020 | 0.5790 (0.3391) |
| 2022 | 0.8200 (0.3620) |
| 2023 | 0.7710 (0.2640) |
