| Year | Value (SE) |
|---|---|
| 2008 | 0.8637 (0.1679) |
| 2009 | 0.6997 (0.0413) |
| 2010 | 0.7798 (0.0836) |
| 2011 | 0.7748 (0.0415) |
| 2012 | 0.6826 (0.0308) |
| 2013 | 0.8016 (0.1014) |
| 2014 | 0.8011 (0.0967) |
| 2015 | 0.7956 (0.1979) |
| 2016 | 0.7761 (0.0320) |
| 2017 | 0.8818 (0.0548) |
| 2019 | 0.8829 (0.0923) |
| 2020 | 1.0888 (0.2743) |
| 2021 | 2.1530 (2.1241) |
