Data quality control procedures
| Quality control procedure | Data quality criteria | Frequency of records (percentage of 39 included studies) | Reference no |
| Predefined quality criteria for data | Completeness Accuracy | 5 (12.82) | 26 27 36 37 53 |
| Cross review checking | Accuracy Consistency Completeness | 8 (20.51) | 26 27 36 37 44 50 53 54 58 |
| Checking for missing data | Completeness Adequacy | 6 (15.38) | 12 33 36 44 54 58 |
| Checking for duplications | Adequacy Accuracy | 3 (7.69) | 12 44 54 58 |
| Unification of data formats | Consistency | 5 (12.82) | 27 33 36 53 58 |
| Double entry of part of all data | Accuracy | 7 (17.94) | 26 27 36 37 44 53 54 58 |