| Year | Value (SE) |
|---|---|
| 2009 | 0.7870 (0.0102) |
| 2010 | 0.7170 (0.0354) |
| 2011 | 0.7190 (0.0083) |
| 2012 | 0.6460 (0.0106) |
| 2013 | 0.6550 (0.0271) |
| 2014 | 0.8090 (0.0167) |
| 2015 | 0.7540 (0.0409) |
| 2016 | 0.7640 (0.0105) |
| 2018 | 0.7720 (0.0139) |
| 2019 | 0.7010 (0.0074) |
| 2022 | 0.6910 (0.0159) |
| 2023 | 0.7730 (0.0121) |
| 2024 | 0.7650 (0.0383) |
