| Year | Value (SE) |
|---|---|
| 2003 | 0.4120 (0.0994) |
| 2007 | 0.3430 (0.0921) |
| 2008 | 0.4030 (0.0248) |
| 2009 | 0.7530 (0.0796) |
| 2010 | 0.6130 (0.0450) |
| 2011 | 0.6350 (0.0487) |
| 2012 | 0.6890 (0.0561) |
| 2013 | 0.5570 (0.1063) |
| 2014 | 0.7030 (0.1595) |
| 2015 | 0.1810 (0.0318) |
| 2018 | 0.4630 (0.0267) |
| 2019 | 0.3830 (0.0362) |
| 2020 | 0.5520 (0.1773) |
| 2021 | 0.1790 (0.0220) |
| 2022 | 0.3100 (0.0849) |
| 2023 | 0.2980 (0.0376) |
