| Year | Value (SE) |
|---|---|
| 2002 | 0.2850 (0.0374) |
| 2007 | 0.6300 (0.0636) |
| 2008 | 0.6930 (0.0557) |
| 2009 | 0.5790 (0.0532) |
| 2010 | 0.7370 (0.0442) |
| 2011 | 0.6450 (0.0455) |
| 2012 | 0.6230 (0.0463) |
| 2013 | 0.4890 (0.0724) |
| 2014 | 0.6290 (0.1222) |
| 2015 | 0.3050 (0.0558) |
| 2018 | 0.5290 (0.0328) |
| 2019 | 0.4510 (0.0434) |
| 2020 | 0.4190 (0.0867) |
| 2021 | 0.3000 (0.0389) |
| 2022 | 0.4450 (0.1013) |
| 2023 | 0.3430 (0.0445) |
| 2024 | 0.3180 (0.0332) |
