| Year | Value (SE) |
|---|---|
| 2008 | 0.5770 (0.0899) |
| 2009 | 0.5330 (0.0632) |
| 2010 | 0.6270 (0.0466) |
| 2011 | 0.7900 (0.0985) |
| 2012 | 0.5430 (0.0592) |
| 2013 | 0.6630 (0.1013) |
| 2014 | 0.8830 (0.1263) |
| 2015 | 0.4570 (0.0627) |
| 2016 | 0.6970 (0.0518) |
| 2017 | 0.7690 (0.0622) |
| 2019 | 0.7030 (0.1721) |
| 2020 | 1.3730 (0.2575) |
| 2021 | 0.5790 (0.1042) |
