| Year | Value (SE) |
|---|---|
| 2008 | 0.8944 (0.0992) |
| 2009 | 0.9575 (0.0559) |
| 2010 | 0.8342 (0.1167) |
| 2011 | 0.9249 (0.0309) |
| 2012 | 0.9438 (0.0433) |
| 2013 | 0.8300 (0.0707) |
| 2014 | 0.8584 (0.0474) |
| 2015 | 0.7952 (0.1525) |
| 2016 | 0.8670 (0.0447) |
| 2017 | 0.9561 (0.0821) |
| 2018 | 0.9692 (0.0808) |
| 2019 | 0.8678 (0.0850) |
| 2020 | 1.2793 (0.4870) |
| 2021 | 1.3212 (0.9677) |
| 2022 | 1.6765 (0.6045) |
| 2023 | 0.6319 (0.1479) |
