Reason for misclassification of cases and controls
| Type of misclassification | Unit 1 (Umbria) | Unit 2 (ASL Napoli 3 Sud) | Unit 3 (Friuli Venezia Giulia) | |
| Invasive breast cancer | ||||
| False positives | ||||
| 1 | Histological examination missing | 6 | 8 | 8 |
| 2 | Negative histology | 4 | 1 | 1 |
| (1) Carcinoma in situ | 2 | 1 | ||
| Total | 10 | 9 | 9 | |
| False negative | ||||
| 1 | Possible breast cancer relapse | 1 | 1 | – |
| 2 | Metastatic breast cancer | 2 | 4 | – |
| Total | 3 | 5 | – | |
| Breast carcinoma in situ | ||||
| False positives | ||||
| 1 | Histological examination missing | – | 8 | 2 |
| 2 | Negative histology | 2 | 7 | 9 |
| Total | 2 | 15 | 11 | |
| False negative | ||||
| 1 | Possible carcinoma in situ | – | – | – |