| Year | Value (SE) |
|---|---|
| 2008 | 0.6245 (0.0544) |
| 2009 | 0.7743 (0.0461) |
| 2010 | 0.7212 (0.0950) |
| 2011 | 0.6072 (0.0188) |
| 2013 | 0.4628 (0.0772) |
| 2014 | 0.7028 (0.1104) |
| 2015 | 0.5300 (0.2243) |
| 2016 | 0.6589 (0.0696) |
| 2017 | 0.5880 (0.0503) |
| 2018 | 0.9202 (0.1822) |
| 2019 | 0.7042 (0.0963) |
| 2020 | 0.5214 (0.2743) |
| 2021 | 0.4269 (0.1658) |
| 2023 | 0.4680 (0.1487) |
| 2024 | 0.6070 (0.2917) |
