Table 1.
Scenarios involving different combinations of patient identifiers that resulted in false matches (n=176, 0.1%)
| Sex (100% valid) | Date of birth (100% valid) | NHS number (58.5% valid) | Hospital (100% valid) | Local ID (100% valid) | Postcode (98.3% valid) | False matches n (%) | |
|---|---|---|---|---|---|---|---|
| Scenarios involving NHS numbers that differ | |||||||
| 1 | 1 | 0* | 0 | 0 | 0 | 20 (11.8) | |
| 1 | 1 | 0* | 0 | 0 | 1 | 70 (41.4) | |
| 1 | 1 | 0* | 1 | 0 | 0 | 1 (0.6) | |
| 1 | 1 | 0* | 1 | 0 | 1 | 39 (23.8) | |
| 1 | 1 | 0* | 1 | 1 | 1 | 1 (0.6) | =131 (74.4%) |
| Scenarios involving NHS numbers that match | |||||||
| 1 | 1 | 1 | 0 | 0 | 0 | 33 (19.5) | |
| 1 | 1 | 1 | 1 | 0 | 0 | 4 (2.4) | |
| 1 | 1 | 1 | 1 | 1 | 0 | 1 (0.6) | =38 (21.6%) |
| Other scenarios† | 7 (4.0) | =7 (5%) | |||||
1=identifier is the same, 0=identifier is different or missing.
*Records with missing NHS numbers are linked by the HESID algorithm, unless a different NHS number is present.
†These scenarios occur when a record has an NHS number (and can therefore link to other records) but is compared to an initial record where the NHS number is missing and the postcode is different. The initial record itself can be linked to other records that have the same postcode.
HESID, Hospital Episode Statistics ID; NHS, National Health Service.