| Year | Value (SE) |
|---|---|
| 2008 | 0.5565 (0.0737) |
| 2009 | 0.4330 (0.0518) |
| 2013 | 0.4176 (0.0803) |
| 2014 | 0.4455 (0.1096) |
| 2015 | 0.3187 (0.1347) |
| 2016 | 0.3627 (0.0632) |
| 2017 | 0.5590 (0.0665) |
| 2018 | 0.4281 (0.1201) |
| 2019 | 0.2860 (0.0701) |
| 2020 | 0.2426 (0.1296) |
| 2021 | 0.5251 (0.5361) |
| 2022 | 0.3371 (0.1943) |
| 2023 | 0.3553 (0.2140) |
