| Year | Value (SE) |
|---|---|
| 2003 | 0.4020 (0.0232) |
| 2004 | 0.4940 (0.0823) |
| 2005 | 0.3240 (0.0346) |
| 2012 | 0.4849 (0.0331) |
| 2013 | 0.3372 (0.0361) |
| 2014 | 0.4492 (0.0763) |
| 2015 | 0.2976 (0.0333) |
| 2016 | 0.4852 (0.0275) |
| 2017 | 0.3669 (0.0609) |
| 2018 | 0.3496 (0.0482) |
| 2019 | 0.3966 (0.0516) |
| 2020 | 0.4913 (0.1250) |
