| Year | Value (SE) |
|---|---|
| 2008 | 0.8650 (0.0341) |
| 2009 | 0.7970 (0.0074) |
| 2010 | 0.7970 (0.0207) |
| 2011 | 0.7040 (0.0082) |
| 2012 | 0.7000 (0.0075) |
| 2013 | 0.7420 (0.0133) |
| 2014 | 0.7910 (0.0111) |
| 2015 | 0.8470 (0.0372) |
| 2016 | 0.7870 (0.0088) |
| 2017 | 0.7870 (0.0132) |
| 2018 | 0.8150 (0.0102) |
| 2019 | 0.7330 (0.0110) |
| 2020 | 0.7830 (0.0104) |
| 2021 | 0.7680 (0.0104) |
| 2022 | 0.7320 (0.0110) |
| 2023 | 0.6810 (0.0088) |
| 2024 | 0.7830 (0.0175) |
