Linkage performance in claims dataset of 32 991 571 claims encounters
| Linkage step | Linkage rule*† | Number of flexible fields for matching | Total linked Hospitalisations | Uniqueness‡ |
| 1 | Age at admission (±1 year), date of admission (±1 day), date of discharge (±1 day), sex, state, and primary diagnosis, by hospital ID | 3 | 17 850 | 89.6 |
| 2 | Age at admission, date of admission (±1 day), date of discharge, sex, state, and primary diagnosis, by hospital ID | 1 | 10 917 | 98.0 |
| 3 | Age at admission, date of admission, date of discharge (±1 day), sex, state, and primary diagnosis, by hospital ID | 1 | 10 445 | 98.0 |
| 4 | Age at admission (±1 year), date of admission, date of discharge, sex, state, and primary diagnosis, by hospital ID | 1 | 14 004 | 98.0 |
| 5 | Age at admission, date of admission, date of discharge, sex, state, and primary diagnosis, by hospital ID | 0 | 10 079 | 99.1 |
*Unless otherwise specified, linkage rules employed exact matching of linking fields.
†Optum Clinformatics only includes year of birth for commercial beneficiaries, thus the linking field age at admission was always allowed to differ by 1 year.
‡Uniqueness = (1−(N multiple hospitalisations in claims+N multiple hospitalisations in registry))/N linked hospitalisations] *100