| 压力 分级 | 1年 | 2年 | 3年 | 4年 | ≥5年 | |||||
| 试验组 | 对照组 | 试验组 | 对照组 | 试验组 | 对照组 | 试验组 | 对照组 | 试验组 | 对照组 | |
| 没有 | 0 | 1 (2%) | 4 (8%) | 3 (7%) | 21 (53%) | 10 (20%) | 68 (56%) | 53 (46%) | 139 (72%) | 128 (66%) |
| 轻度 | 36 (67%) | 10 (21%) | 30 (60%) | 13 (31%) | 12 (30%) | 27 (53%) | 46 (38%) | 52 (45%) | 50 (26%) | 59 (30%) |
| 中度 | 19 (33%) | 26 (54%) | 16 (42%) | 19 (45%) | 7 (17%) | 12 (23%) | 7 (6%) | 10 (9%) | 5 (2%) | 8 (4%) |
| 偏重 | 0 | 5 (10%) | 0 | 5 (12%) | 0 | 2 (4%) | 0 | 0 | 0 | 0 |
| 严重 | 0 | 6 (13%) | 0 | 2 (5%) | 0 | 0 | 0 | 0 | 0 | 0 |
| χ值 | 27.734 | 14.411 | 11.287 | 2.600 | 1.877 | |||||
| p值 | 0.000 | 0.002 | 0.006 | 0.280 | 0.429 | |||||