| Year | Value (SE) |
|---|---|
| 2008 | 0.8440 (0.0672) |
| 2009 | 0.9120 (0.0495) |
| 2010 | 0.8540 (0.1235) |
| 2011 | 0.7970 (0.0235) |
| 2013 | 0.7620 (0.1193) |
| 2014 | 0.8580 (0.1263) |
| 2015 | 0.9820 (0.3563) |
| 2016 | 0.8160 (0.0774) |
| 2017 | 0.7930 (0.0645) |
| 2018 | 1.1080 (0.2148) |
| 2019 | 0.7580 (0.0997) |
| 2020 | 0.3850 (0.1940) |
| 2021 | 0.5400 (0.1956) |
| 2023 | 0.5460 (0.1634) |
| 2024 | 1.3940 (0.5717) |
