| Year | Value (SE) |
|---|---|
| 2009 | 0.6165 (0.0547) |
| 2010 | 0.5759 (0.1152) |
| 2011 | 0.4806 (0.0249) |
| 2012 | 0.4997 (0.0434) |
| 2013 | 0.4494 (0.0677) |
| 2014 | 0.7404 (0.0839) |
| 2015 | 0.6145 (0.1651) |
| 2016 | 0.5200 (0.0433) |
| 2018 | 0.5466 (0.0814) |
| 2019 | 0.5444 (0.0443) |
| 2022 | 0.4132 (0.2072) |
| 2023 | 0.3987 (0.0909) |
| 2024 | 0.3583 (0.1427) |
