| Year | Value (SE) |
|---|---|
| 2007 | 0.6530 (0.0148) |
| 2009 | 0.6270 (0.0116) |
| 2010 | 0.7460 (0.0306) |
| 2011 | 0.7300 (0.0139) |
| 2012 | 0.6520 (0.0126) |
| 2013 | 0.5830 (0.0163) |
| 2014 | 0.5950 (0.0112) |
| 2015 | 0.5310 (0.0271) |
| 2016 | 0.6840 (0.0117) |
| 2018 | 0.6340 (0.0304) |
| 2019 | 0.5670 (0.0220) |
| 2020 | 0.7450 (0.0286) |
| 2021 | 0.7990 (0.0410) |
| 2022 | 0.7570 (0.0349) |
| 2023 | 0.8030 (0.0249) |
