| 时间 | 平均 | 最高 | 最低 |
|---|---|---|---|
| 2021 | 6.69 | 7.67 | 6.29 |
| 2020 | 6.04 | 6.99 | 4.83 |
| 2019 | 6.07 | 7.3 | 5 |
| 2018 | 6.68 | 9.32 | 5.05 |
| 2017 | 7.89 | 9.24 | 6.99 |
| 2016 | 8.07 | 9.27 | 7.2 |
| 2015 | 8.79 | 12.87 | 6.51 |
| 2014 | 5.49 | 8.55 | 4.87 |
| 2013 | 6.36 | 8.17 | 5.25 |
| 2012 | 7.68 | 10.43 | 5.71 |
| 2011 | 11.58 | 16.07 | 8.7 |
| 2010 | 16.51 | 23.77 | 12.75 |
| 2009 | 19.41 | 25.43 | 10.63 |
| 2008 | 17.07 | 33.42 | 10.27 |