| Year | Value (SE) |
|---|---|
| 2000 | 0.1830 (0.0306) |
| 2001 | 0.1870 (0.0105) |
| 2002 | 0.3040 (0.0275) |
| 2003 | 0.2680 (0.0110) |
| 2004 | 0.1350 (0.0170) |
| 2007 | 0.2630 (0.0128) |
| 2010 | 0.2630 (0.0279) |
| 2011 | 0.2350 (0.0290) |
| 2012 | 0.2800 (0.0227) |
| 2013 | 0.2360 (0.0291) |
| 2014 | 0.2900 (0.0360) |
| 2015 | 0.2490 (0.0462) |
| 2016 | 0.2420 (0.0201) |
| 2017 | 0.2070 (0.0188) |
| 2018 | 0.2590 (0.0165) |
| 2022 | 0.1890 (0.0625) |
| 2023 | 0.0890 (0.0235) |
