| Year | Value (SE) |
|---|---|
| 2008 | 0.5348 (0.0829) |
| 2009 | 0.6465 (0.0403) |
| 2010 | 0.5824 (0.0579) |
| 2011 | 0.5391 (0.0396) |
| 2012 | 0.5761 (0.0404) |
| 2013 | 0.5076 (0.0426) |
| 2014 | 0.5724 (0.0533) |
| 2015 | 0.6790 (0.1042) |
| 2016 | 0.6071 (0.0378) |
| 2017 | 0.6303 (0.0591) |
| 2018 | 0.6178 (0.0675) |
| 2019 | 0.5641 (0.0536) |
| 2020 | 0.7054 (0.1588) |
| 2021 | 0.5923 (0.1730) |
| 2022 | 0.5908 (0.1661) |
| 2023 | 0.4270 (0.0704) |
| 2024 | 0.9320 (0.4175) |
