| Year | Value (SE) |
|---|---|
| 2008 | 0.6806 (0.1380) |
| 2009 | 0.4424 (0.0691) |
| 2013 | 0.5463 (0.1401) |
| 2014 | 0.3179 (0.0951) |
| 2015 | 0.4139 (0.1445) |
| 2016 | 0.5032 (0.1492) |
| 2017 | 0.6960 (0.0979) |
| 2018 | 0.5961 (0.1901) |
| 2019 | 0.4762 (0.1354) |
| 2020 | 0.6602 (0.3753) |
| 2021 | 0.5524 (0.5744) |
| 2022 | 0.8966 (0.6365) |
| 2023 | 0.7933 (0.3622) |
