| Year | Value (SE) |
|---|---|
| 2008 | 0.8000 (0.0159) |
| 2009 | 0.9310 (0.0073) |
| 2010 | 0.7900 (0.0529) |
| 2011 | 0.7950 (0.0049) |
| 2013 | 0.6710 (0.0281) |
| 2014 | 0.8700 (0.0333) |
| 2015 | 0.6970 (0.0613) |
| 2016 | 0.8460 (0.0161) |
| 2017 | 0.8650 (0.0154) |
| 2018 | 0.8390 (0.0232) |
| 2019 | 0.9290 (0.0252) |
| 2020 | 0.8380 (0.0176) |
| 2021 | 0.7020 (0.0104) |
| 2023 | 0.7960 (0.0209) |
| 2024 | 0.7520 (0.0258) |
