| Year | Value (SE) |
|---|---|
| 2000 | 0.7920 (0.0154) |
| 2001 | 0.7600 (0.0073) |
| 2008 | 0.8290 (0.0096) |
| 2009 | 0.8320 (0.0042) |
| 2010 | 0.8100 (0.0128) |
| 2011 | 0.7970 (0.0051) |
| 2012 | 0.7490 (0.0063) |
| 2013 | 0.8180 (0.0189) |
| 2014 | 0.8500 (0.0107) |
| 2015 | 0.8430 (0.0368) |
| 2016 | 0.7940 (0.0095) |
| 2017 | 0.7360 (0.0066) |
| 2018 | 0.7600 (0.0086) |
| 2019 | 0.8000 (0.0057) |
| 2020 | 0.7830 (0.0081) |
| 2021 | 0.8390 (0.0098) |
| 2022 | 0.7550 (0.0082) |
| 2023 | 0.8450 (0.0093) |
