| Year | Value (SE) |
|---|---|
| 2003 | 0.2021 (0.0271) |
| 2004 | 0.1249 (0.0230) |
| 2005 | 0.2151 (0.0287) |
| 2006 | 0.1165 (0.0184) |
| 2008 | 0.3157 (0.0867) |
| 2009 | 0.3327 (0.0848) |
| 2010 | 0.2261 (0.0487) |
| 2011 | 0.2216 (0.0593) |
| 2013 | 0.4714 (0.1003) |
| 2014 | 0.3679 (0.0924) |
| 2015 | 0.0887 (0.0458) |
| 2019 | 0.2530 (0.0858) |
| 2020 | 0.3318 (0.2406) |
| 2023 | 0.5576 (0.3441) |
