| Year | Value (SE) |
|---|---|
| 2008 | 0.7204 (0.1669) |
| 2009 | 0.6017 (0.0590) |
| 2010 | 0.6893 (0.0857) |
| 2011 | 0.5974 (0.0504) |
| 2012 | 0.6410 (0.0679) |
| 2013 | 0.6974 (0.1180) |
| 2014 | 0.6930 (0.1114) |
| 2015 | 0.5721 (0.1505) |
| 2016 | 0.8467 (0.0586) |
| 2017 | 0.8377 (0.1147) |
| 2019 | 1.0489 (0.3584) |
| 2020 | 0.7904 (0.2743) |
| 2021 | 0.9064 (0.9224) |
