| Year | Value (SE) |
|---|---|
| 2008 | 0.7320 (0.1418) |
| 2009 | 0.7820 (0.1479) |
| 2010 | 0.6330 (0.0925) |
| 2011 | 0.9660 (0.1084) |
| 2012 | 0.7270 (0.0788) |
| 2013 | 0.8590 (0.1403) |
| 2014 | 0.6630 (0.0968) |
| 2015 | 0.5280 (0.0767) |
| 2016 | 0.4230 (0.0484) |
| 2018 | 0.5120 (0.0822) |
| 2019 | 0.7070 (0.1195) |
| 2020 | 0.7530 (0.1687) |
| 2022 | 0.4360 (0.1315) |
| 2023 | 0.6080 (0.0972) |
