| Year | Value (SE) |
|---|---|
| 2000 | 0.3460 (0.0741) |
| 2006 | 0.6520 (0.0656) |
| 2008 | 0.7320 (0.0341) |
| 2009 | 0.7050 (0.0441) |
| 2010 | 0.7350 (0.0336) |
| 2011 | 0.7700 (0.0315) |
| 2012 | 0.5000 (0.0611) |
| 2013 | 0.6510 (0.0276) |
| 2014 | 0.7830 (0.0433) |
| 2016 | 0.6780 (0.0247) |
| 2017 | 0.6310 (0.0314) |
| 2018 | 0.5830 (0.0324) |
| 2019 | 0.3880 (0.0218) |
| 2020 | 0.3110 (0.0281) |
| 2021 | 0.3240 (0.0441) |
| 2022 | 0.5030 (0.0736) |
| 2023 | 0.3580 (0.0333) |
| 2024 | 0.2320 (0.0324) |
