| Year | Value (SE) |
|---|---|
| 2001 | 0.0590 (0.0295) |
| 2006 | 0.6700 (0.0343) |
| 2007 | 0.5710 (0.0512) |
| 2008 | 0.4440 (0.0263) |
| 2009 | 0.4990 (0.0404) |
| 2010 | 0.6130 (0.0454) |
| 2011 | 0.5920 (0.0545) |
| 2012 | 0.7870 (0.0693) |
| 2013 | 0.5470 (0.0999) |
| 2014 | 0.4600 (0.1102) |
| 2015 | 0.4270 (0.2012) |
| 2016 | 0.4310 (0.1172) |
| 2018 | 0.4490 (0.0472) |
| 2020 | 0.3740 (0.0716) |
| 2021 | 0.2410 (0.0380) |
| 2022 | 0.3060 (0.0788) |
| 2023 | 0.3590 (0.0647) |
| 2024 | 0.2420 (0.0445) |
