| Year | Value (SE) |
|---|---|
| 2008 | 0.8720 (0.0971) |
| 2009 | 0.8810 (0.0370) |
| 2010 | 0.7080 (0.1846) |
| 2011 | 0.8340 (0.0268) |
| 2012 | 0.8890 (0.0291) |
| 2013 | 0.9520 (0.0677) |
| 2014 | 1.0060 (0.0458) |
| 2015 | 1.0070 (0.1482) |
| 2016 | 0.7930 (0.0538) |
| 2017 | 0.9030 (0.0820) |
| 2018 | 0.5320 (0.0738) |
| 2019 | 0.7420 (0.1140) |
| 2020 | 0.4560 (0.1516) |
| 2021 | 0.4590 (0.4487) |
| 2022 | 0.8040 (0.2815) |
