| Year | Value (SE) |
|---|---|
| 2008 | 0.6901 (0.1057) |
| 2009 | 0.8120 (0.0504) |
| 2010 | 0.7977 (0.0765) |
| 2011 | 0.7790 (0.0565) |
| 2012 | 0.8528 (0.0591) |
| 2013 | 0.7254 (0.0596) |
| 2014 | 0.7507 (0.0692) |
| 2015 | 0.7321 (0.1080) |
| 2016 | 0.7592 (0.0469) |
| 2017 | 0.7679 (0.0710) |
| 2018 | 0.7475 (0.0813) |
| 2019 | 0.7967 (0.0749) |
| 2020 | 0.9269 (0.2087) |
| 2021 | 0.8428 (0.2462) |
| 2022 | 0.7398 (0.2082) |
| 2023 | 0.6093 (0.1004) |
| 2024 | 1.4392 (0.6446) |
