| Year | Value (SE) |
|---|---|
| 2000 | 0.2250 (0.0281) |
| 2001 | 0.1720 (0.0107) |
| 2002 | 0.2320 (0.0169) |
| 2003 | 0.3230 (0.0311) |
| 2004 | 0.1320 (0.0169) |
| 2007 | 0.2520 (0.0126) |
| 2011 | 0.2990 (0.0440) |
| 2012 | 0.3320 (0.0274) |
| 2013 | 0.2660 (0.0309) |
| 2014 | 0.2280 (0.0211) |
| 2015 | 0.1990 (0.0291) |
| 2016 | 0.2680 (0.0206) |
| 2017 | 0.2460 (0.0259) |
| 2018 | 0.2590 (0.0165) |
| 2022 | 0.2870 (0.1379) |
| 2023 | 0.1960 (0.0269) |
| 2024 | 0.2090 (0.0513) |
