| Year | Value (SE) |
|---|---|
| 2008 | 0.8555 (0.1990) |
| 2009 | 0.8323 (0.0815) |
| 2010 | 0.8574 (0.1070) |
| 2011 | 0.7189 (0.0606) |
| 2012 | 0.8412 (0.0889) |
| 2013 | 0.8547 (0.1450) |
| 2014 | 0.8919 (0.1433) |
| 2015 | 0.7401 (0.1947) |
| 2016 | 0.9811 (0.0679) |
| 2017 | 0.9017 (0.1235) |
| 2019 | 1.2487 (0.4269) |
| 2020 | 0.9213 (0.3197) |
| 2021 | 1.1562 (1.1765) |
