| Year | Value (SE) |
|---|---|
| 2003 | 0.4040 (0.0280) |
| 2004 | 0.3910 (0.0927) |
| 2005 | 0.1660 (0.0355) |
| 2012 | 0.3650 (0.0211) |
| 2013 | 0.3620 (0.0454) |
| 2014 | 0.3500 (0.0663) |
| 2015 | 0.1960 (0.0323) |
| 2016 | 0.3480 (0.0273) |
| 2017 | 0.2790 (0.0303) |
| 2018 | 0.3450 (0.0385) |
| 2019 | 0.3020 (0.0273) |
| 2020 | 0.4500 (0.0619) |
