| Year | Value (SE) |
|---|---|
| 2007 | 0.4888 (0.0417) |
| 2008 | 0.2696 (0.0447) |
| 2009 | 0.3070 (0.0260) |
| 2010 | 0.3169 (0.0464) |
| 2011 | 0.3718 (0.0288) |
| 2012 | 0.3980 (0.0235) |
| 2013 | 0.5841 (0.0510) |
| 2014 | 0.6097 (0.0404) |
| 2015 | 0.5098 (0.0855) |
| 2016 | 0.4743 (0.0229) |
| 2017 | 0.4850 (0.0384) |
| 2018 | 0.3716 (0.0428) |
| 2019 | 0.3206 (0.0430) |
| 2020 | 0.4972 (0.1781) |
| 2021 | 0.4719 (0.4086) |
| 2022 | 0.3441 (0.1111) |
| 2023 | 0.3978 (0.0696) |
| 2024 | 0.3138 (0.3164) |
