| Year | Value (SE) |
|---|---|
| 2008 | 0.4470 (0.0115) |
| 2009 | 0.5060 (0.0062) |
| 2010 | 0.3830 (0.0229) |
| 2011 | 0.4980 (0.0054) |
| 2012 | 0.5810 (0.0055) |
| 2013 | 0.6070 (0.0163) |
| 2014 | 0.7940 (0.0084) |
| 2015 | 0.7720 (0.0362) |
| 2016 | 0.7720 (0.0081) |
| 2017 | 0.7450 (0.0125) |
| 2018 | 0.6360 (0.0150) |
| 2019 | 0.2810 (0.0086) |
| 2020 | 0.5670 (0.0192) |
| 2021 | 0.2840 (0.0116) |
| 2022 | 0.4780 (0.0128) |
