| Year | Value (SE) |
|---|---|
| 2009 | 0.6490 (0.0742) |
| 2010 | 0.6210 (0.0664) |
| 2011 | 0.5530 (0.0357) |
| 2012 | 0.5670 (0.0328) |
| 2013 | 0.6880 (0.0680) |
| 2014 | 0.6640 (0.1244) |
| 2015 | 0.8580 (0.2152) |
| 2016 | 0.6740 (0.0439) |
| 2017 | 0.5300 (0.0410) |
| 2018 | 0.4960 (0.0664) |
| 2019 | 0.4640 (0.0554) |
| 2020 | 0.7710 (0.1149) |
| 2022 | 0.5090 (0.1208) |
| 2023 | 0.5540 (0.0700) |
