| Year | Value (SE) |
|---|---|
| 2006 | 0.7970 (0.0346) |
| 2008 | 0.7460 (0.0419) |
| 2009 | 0.7450 (0.0199) |
| 2010 | 0.7210 (0.0181) |
| 2011 | 0.8700 (0.0157) |
| 2012 | 0.8440 (0.0347) |
| 2015 | 0.6750 (0.0741) |
| 2016 | 0.5600 (0.0501) |
| 2019 | 0.6770 (0.0618) |
| 2020 | 0.5500 (0.0361) |
| 2021 | 0.6110 (0.0223) |
| 2022 | 0.7320 (0.0338) |
| 2023 | 0.5940 (0.0193) |
