Outcome definitions
| Outcome | Definition |
| Length of stay | Time difference in days between admission and discharge dates of the index admission. A binary variable was defined indicating patients whose index length of stay was in the upper quartile across both cohorts. |
| Readmission | A subsequent emergency admission for any cause, within 90 days of the index discharge date. |
| Mortality | For those who died outside hospital, we used the midpoint of their month of death as recorded in the Discover data. Binary outcome variables were defined for death in hospital, death prior to 30 and 90 days postdischarge (including in hospital). |
| Primary care activity | For each patient, the number of days in which at least one clinical code was assigned to their record. Details of the process by which administrative codes were removed from the data, to leave only clinical codes, are provided in online supplemental file 2. |