| Occurrence factors | Cases (n = 236) | % |
| Complications, accidental disease | 77 | 32.6 |
| Personal behavior | 85 | 36.0 |
| Confirmation error | 58 | 24.6 |
| Judgment error | 15 | 6.4 |
| Observation error | 4 | 1.7 |
| Lack of explanation | 4 | 1.7 |
| Insufficient cooperation | 2 | 0.8 |
| Recording deficiencies | 2 | 0.8 |
| Human factor | 37 | 15.7 |
| Immature technique and procedure | 25 | 10.6 |
| Lack of knowledge | 6 | 2.5 |
| Usually with different body conditions | 5 | 2.1 |
| Complicated work situation | 1 | 0.4 |
| Environment equipment | 6 | 2.5 |
| Problem of medical equipment | 4 | 1.7 |
| Problem of drugs | 1 | 0.4 |
| Problem with the system | 1 | 0.4 |
| Others | 31 | 13.1 |