| Year | Value (SE) |
|---|---|
| 2000 | 0.4840 (0.1474) |
| 2001 | 0.2290 (0.0264) |
| 2002 | 0.6260 (0.0568) |
| 2003 | 0.3800 (0.0255) |
| 2004 | 0.3830 (0.0506) |
| 2005 | 0.2260 (0.0320) |
| 2006 | 0.2240 (0.0191) |
| 2007 | 0.3900 (0.0221) |
| 2008 | 0.4990 (0.0895) |
| 2009 | 0.3070 (0.0442) |
| 2010 | 0.5860 (0.1328) |
| 2011 | 0.1470 (0.0321) |
| 2012 | 0.3350 (0.0282) |
| 2013 | 0.3840 (0.0537) |
| 2014 | 0.4830 (0.0895) |
| 2015 | 0.2650 (0.0808) |
| 2016 | 0.3400 (0.0708) |
| 2018 | 0.3650 (0.0668) |
| 2019 | 0.4490 (0.0721) |
| 2020 | 0.3400 (0.0579) |
| 2021 | 0.1910 (0.0686) |
| 2022 | 0.4220 (0.1629) |
| 2023 | 0.3140 (0.0703) |
