| Year | Value (SE) |
|---|---|
| 2008 | 0.9027 (0.1852) |
| 2009 | 0.7819 (0.0752) |
| 2010 | 0.6818 (0.0826) |
| 2011 | 0.8707 (0.0949) |
| 2012 | 0.7736 (0.0744) |
| 2013 | 0.6150 (0.0699) |
| 2014 | 0.6108 (0.0763) |
| 2015 | 0.5475 (0.1028) |
| 2016 | 0.6881 (0.0644) |
| 2017 | 0.6856 (0.0765) |
| 2018 | 0.7284 (0.0961) |
| 2019 | 1.0082 (0.1271) |
| 2020 | 1.0135 (0.2476) |
| 2021 | 0.7326 (0.2576) |
| 2022 | 0.8006 (0.2920) |
| 2023 | 0.6627 (0.1239) |
| 2024 | 0.6285 (0.3153) |
