| Year | Value (SE) |
|---|---|
| 2008 | 0.9690 (0.0849) |
| 2009 | 0.9110 (0.0467) |
| 2010 | 0.8060 (0.1061) |
| 2011 | 0.9130 (0.0287) |
| 2012 | 0.9710 (0.0427) |
| 2013 | 0.7860 (0.0616) |
| 2014 | 0.8840 (0.0466) |
| 2015 | 0.6750 (0.1198) |
| 2016 | 1.0260 (0.0468) |
| 2017 | 0.9580 (0.0784) |
| 2018 | 0.9840 (0.0761) |
| 2019 | 0.8050 (0.0762) |
| 2020 | 1.3410 (0.4264) |
| 2021 | 0.5360 (0.3627) |
| 2022 | 1.5090 (0.5063) |
| 2023 | 0.7650 (0.1606) |
