| Year | Value (SE) |
|---|---|
| 2000 | 0.3900 (0.0190) |
| 2001 | 0.2480 (0.0048) |
| 2002 | 0.3330 (0.0082) |
| 2003 | 0.2230 (0.0097) |
| 2004 | 0.2270 (0.0089) |
| 2007 | 0.3440 (0.0094) |
| 2010 | 0.3420 (0.0131) |
| 2011 | 0.3570 (0.0129) |
| 2012 | 0.4090 (0.0127) |
| 2013 | 0.3950 (0.0159) |
| 2014 | 0.3860 (0.0168) |
| 2015 | 0.2870 (0.0210) |
| 2016 | 0.4210 (0.0136) |
| 2017 | 0.2840 (0.0140) |
| 2018 | 0.2920 (0.0110) |
| 2022 | 0.5600 (0.1801) |
| 2023 | 0.3530 (0.0477) |
| 2024 | 0.3570 (0.0619) |
