| Year | Value (SE) |
|---|---|
| 2008 | 0.5470 (0.0849) |
| 2009 | 0.3270 (0.0339) |
| 2013 | 0.2700 (0.0459) |
| 2014 | 0.2120 (0.0384) |
| 2015 | 0.3190 (0.0474) |
| 2016 | 0.3430 (0.0828) |
| 2017 | 0.5270 (0.0400) |
| 2018 | 0.4050 (0.0621) |
| 2019 | 0.2110 (0.0308) |
| 2020 | 0.3360 (0.0664) |
| 2021 | 0.3400 (0.0666) |
| 2022 | 0.6400 (0.2661) |
| 2023 | 0.5280 (0.0973) |
