| Year | Value (SE) |
|---|---|
| 2008 | 0.3030 (0.0450) |
| 2009 | 0.4260 (0.0390) |
| 2010 | 0.2370 (0.0302) |
| 2011 | 0.2710 (0.0195) |
| 2012 | 0.4350 (0.0244) |
| 2013 | 0.4330 (0.0328) |
| 2014 | 0.5790 (0.0367) |
| 2015 | 0.6460 (0.1242) |
| 2016 | 0.4190 (0.0394) |
| 2017 | 0.5430 (0.0394) |
| 2018 | 0.3750 (0.0537) |
| 2019 | 0.1460 (0.0268) |
| 2020 | 0.2840 (0.0343) |
| 2021 | 0.2550 (0.0849) |
| 2022 | 0.3200 (0.0722) |
