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| Methods | Retrospective cohort, ground comparison group only | |
| Participants | People with trauma in the 2007 NTDB, USA | |
| Interventions | HEMS vs. GEMS interfacility transfer to higher level trauma centers | |
| Outcomes | Mortality | |
| Notes | Crew configurations unknown | |
| Risk of bias | ||
| Bias | Authors' judgement | Support for judgement |
| Reporting bias | Low risk | 8/11 |
| External validity | High risk | 1/3 |
| Internal validity | High risk | 4/7 |
| Internal validity: confounding and selection bias | High risk | 2/6 |
| Power | High risk | 0/5 |
