年份 | 2012 | 2013 | 2014 | 2015 | 2016 | 2017 | 2018 | 合计 |
频数 | 13 | 10 | 5 | 34 | 8 | 32 | 481 | 583 |
比例 | 2.23% | 1.72% | 0.86% | 5.83% | 1.37% | 5.49% | 82.50% | 100% |