| 2013年之前 | 2013年之后(包括2013) | 总篇数 | 占比 | ||||
| 编码 | 频数 | 编码 | 频数 | ||||
| 研究方法 | 定量 | 4, 5, 8~11.13, 14, 17, 18, 20 | 11 | 21, 22, 24, 25, 27~31, 36, 37, 39, 40, 42~45 | 17 | 28 | 60.90% |
| 定性 | 1~3, 6, 7, 12, 15, 16, 19 | 9 | 23, 26, 32~35, 38, 41, 46 | 9 | 18 | 39.10% | |
| 研究内容 | 原因 | 8, 10, 12, 14~17 | 7 | 21, 23, 27, 30, 34, 36 | 10 | 17 | 37.00% |
| 路径 | 1~3, 4, 6~14, 16~20 | 18 | 21~30, 32~44 | 23 | 41 | 89.10% | |
| 评价 | 0 | 26, 27, 30~32, 35-37, 39~42, 44 | 12 | 12 | 26.10% | ||