| Year | Value (SE) |
|---|---|
| 2008 | 0.6853 (0.1885) |
| 2009 | 0.7366 (0.1127) |
| 2010 | 0.7794 (0.1129) |
| 2011 | 0.9511 (0.1427) |
| 2012 | 0.7117 (0.1078) |
| 2013 | 0.8120 (0.1851) |
| 2014 | 1.1353 (0.2439) |
| 2015 | 0.5913 (0.1752) |
| 2016 | 0.8075 (0.0818) |
| 2017 | 0.8278 (0.1315) |
| 2019 | 0.8366 (0.3514) |
| 2020 | 1.6002 (0.6309) |
| 2021 | 0.7376 (0.7623) |
