| Year | Value (SE) |
|---|---|
| 2002 | 0.2727 (0.0230) |
| 2004 | 0.3988 (0.0407) |
| 2005 | 0.3425 (0.0416) |
| 2007 | 0.4469 (0.0575) |
| 2008 | 0.4038 (0.0312) |
| 2009 | 0.2463 (0.0187) |
| 2010 | 0.1406 (0.0083) |
| 2011 | 0.6509 (0.0152) |
| 2012 | 0.4539 (0.0078) |
| 2013 | 0.4983 (0.0166) |
| 2014 | 0.4865 (0.0298) |
| 2015 | 0.9207 (0.3881) |
