| Year | Value (SE) |
|---|---|
| 2008 | 0.8876 (0.1507) |
| 2009 | 0.7980 (0.0881) |
| 2010 | 0.8124 (0.1257) |
| 2011 | 0.9093 (0.0722) |
| 2012 | 0.8836 (0.0664) |
| 2013 | 0.7019 (0.0854) |
| 2014 | 0.7222 (0.0635) |
| 2015 | 0.4502 (0.1031) |
| 2016 | 0.7890 (0.0558) |
| 2017 | 0.7884 (0.0825) |
| 2018 | 0.7400 (0.0844) |
| 2019 | 1.0497 (0.1641) |
| 2020 | 1.0929 (0.3917) |
| 2021 | 0.5794 (0.4043) |
| 2022 | 3.0829 (1.6945) |
| 2023 | 0.5676 (0.1415) |
