| Year | Value (SE) |
|---|---|
| 2000 | 0.3520 (0.0260) |
| 2001 | 0.2350 (0.0048) |
| 2002 | 0.3090 (0.0104) |
| 2003 | 0.3170 (0.0061) |
| 2004 | 0.1880 (0.0089) |
| 2007 | 0.3060 (0.0080) |
| 2010 | 0.2950 (0.0147) |
| 2011 | 0.2470 (0.0123) |
| 2012 | 0.3860 (0.0172) |
| 2013 | 0.2970 (0.0168) |
| 2014 | 0.2790 (0.0143) |
| 2015 | 0.2580 (0.0203) |
| 2016 | 0.2740 (0.0122) |
| 2017 | 0.2430 (0.0154) |
| 2018 | 0.2920 (0.0110) |
| 2022 | 0.6870 (0.3354) |
| 2023 | 0.1070 (0.0203) |
