| Year | Value (SE) |
|---|---|
| 2002 | 0.6960 (0.0119) |
| 2007 | 0.8470 (0.0240) |
| 2008 | 0.8610 (0.0158) |
| 2009 | 0.9100 (0.0170) |
| 2010 | 0.9710 (0.0305) |
| 2011 | 0.9000 (0.0116) |
| 2012 | 0.8440 (0.0128) |
| 2013 | 0.8550 (0.0242) |
| 2014 | 0.7250 (0.0211) |
| 2015 | 0.7850 (0.0362) |
| 2018 | 0.8010 (0.0197) |
| 2019 | 0.6870 (0.0208) |
| 2020 | 0.7840 (0.0300) |
| 2021 | 0.6610 (0.0134) |
| 2022 | 0.8370 (0.0248) |
| 2023 | 0.8230 (0.0149) |
| 2024 | 0.7350 (0.0235) |
