| Year | Value (SE) |
|---|---|
| 2006 | 0.5683 (0.0348) |
| 2007 | 0.6395 (0.1110) |
| 2008 | 0.3731 (0.0399) |
| 2009 | 0.6867 (0.0598) |
| 2010 | 0.6698 (0.1037) |
| 2011 | 0.3195 (0.0255) |
| 2012 | 0.3225 (0.0585) |
| 2013 | 0.1761 (0.1084) |
| 2014 | 0.1891 (0.0522) |
| 2016 | 0.2782 (0.0395) |
| 2017 | 0.1965 (0.0422) |
| 2018 | 0.4113 (0.0871) |
| 2019 | 0.3611 (0.0926) |
| 2020 | 0.4524 (0.4141) |
