| 年份 | 样本(家) | 均值 | 中位数 |
| 2012 | 179 | 10.42% | 11.02% |
| 2013 | 179 | 8.64% | 8.95% |
| 2014 | 179 | 7.66% | 7.70% |
| 2015 | 179 | 10.41% | 10.77% |
| 2016 | 180 | 13.12% | 13.49% |
| 2017 | 179 | 8.87% | 8.67% |
| 2018 | 178 | 10.41% | 10.34% |
| 2019 | 178 | 11.01% | 10.68% |
| 2020 | 179 | 11.11% | 10.45% |
| 2021 | 179 | 10.31% | 5.32% |
| 平均 |
| 10.20% | 9.74% |