| Year | Value (SE) |
|---|---|
| 2000 | 0.3280 (0.0164) |
| 2001 | 0.2130 (0.0046) |
| 2002 | 0.2450 (0.0072) |
| 2003 | 0.3220 (0.0112) |
| 2004 | 0.1830 (0.0088) |
| 2007 | 0.2990 (0.0084) |
| 2011 | 0.2650 (0.0136) |
| 2012 | 0.3840 (0.0157) |
| 2013 | 0.2880 (0.0152) |
| 2014 | 0.2880 (0.0150) |
| 2015 | 0.2620 (0.0181) |
| 2016 | 0.3180 (0.0135) |
| 2017 | 0.3030 (0.0229) |
| 2018 | 0.2920 (0.0110) |
| 2022 | 0.2900 (0.0915) |
| 2023 | 0.3090 (0.0567) |
| 2024 | 0.2090 (0.0321) |
