2008 | 2009 | 2010 | 2014 | 2015 | 2016 | 2017 | 2018 | 2019 | 2020 | 2021 |
6.0 | 5.5 | 5.5 | 6.5 | 6.7 | 7.0 | 7.7 | 8.0 | 8.1 | 4.8 | 5.8 |