| Year | Value (SE) |
|---|---|
| 2012 | 0.8030 (0.0124) |
| 2013 | 0.6500 (0.0197) |
| 2014 | 0.8610 (0.0151) |
| 2015 | 0.7600 (0.0346) |
| 2016 | 0.8470 (0.0118) |
| 2017 | 0.8940 (0.0129) |
| 2018 | 0.8370 (0.0126) |
| 2019 | 0.7740 (0.0097) |
| 2020 | 0.8150 (0.0104) |
| 2021 | 0.7980 (0.0095) |
| 2022 | 0.7330 (0.0132) |
| 2023 | 0.8050 (0.0116) |
| 2024 | 0.8310 (0.0220) |
