| Year | Value (SE) |
|---|---|
| 2008 | 0.8010 (0.1519) |
| 2009 | 0.8850 (0.1236) |
| 2010 | 0.9090 (0.0873) |
| 2011 | 1.3230 (0.1843) |
| 2012 | 0.8460 (0.1219) |
| 2013 | 0.9500 (0.1787) |
| 2014 | 1.2730 (0.2228) |
| 2015 | 0.7990 (0.1261) |
| 2016 | 0.8230 (0.0756) |
| 2017 | 0.9180 (0.1330) |
| 2019 | 0.6700 (0.2715) |
| 2020 | 1.7370 (0.5224) |
| 2021 | 0.6380 (0.1943) |
