| Year | Value (SE) |
|---|---|
| 2006 | 0.6625 (0.1074) |
| 2007 | 0.9314 (0.1725) |
| 2008 | 0.6302 (0.1339) |
| 2009 | 0.5602 (0.0950) |
| 2010 | 0.7003 (0.1331) |
| 2011 | 0.5403 (0.0914) |
| 2012 | 0.8011 (0.0686) |
| 2013 | 0.7425 (0.1077) |
| 2014 | 0.9321 (0.1599) |
| 2015 | 0.6395 (0.1982) |
| 2016 | 0.6367 (0.0863) |
| 2017 | 0.8337 (0.1213) |
| 2018 | 0.6190 (0.1009) |
| 2019 | 1.6425 (0.6874) |
| 2020 | 0.6889 (0.2608) |
| 2021 | 0.8974 (0.7139) |
| 2022 | 1.1783 (0.6314) |
| 2023 | 0.4806 (0.1129) |
| 2024 | 0.5341 (0.3071) |
