| Year | Value (SE) |
|---|---|
| 2007 | 0.5371 (0.0420) |
| 2008 | 0.2889 (0.0321) |
| 2009 | 0.3972 (0.0303) |
| 2010 | 0.3903 (0.0550) |
| 2011 | 0.5365 (0.0227) |
| 2012 | 0.4044 (0.0168) |
| 2013 | 0.5961 (0.0394) |
| 2014 | 0.6364 (0.0326) |
| 2015 | 0.6494 (0.1027) |
| 2016 | 0.5470 (0.0199) |
| 2017 | 0.5300 (0.0279) |
| 2018 | 0.4461 (0.0372) |
| 2019 | 0.4496 (0.0443) |
| 2020 | 0.8370 (0.2827) |
| 2021 | 0.8442 (0.7234) |
| 2022 | 0.6156 (0.1347) |
| 2023 | 0.5241 (0.0572) |
| 2024 | 0.5604 (0.5595) |
