Cunningham 1997.

Methods	Retrospective cohort, ground comparison group only
Participants	People with trauma in North Carolina, USA, 1987‐1993
Interventions	HEMS vs. GEMS transport to level I or level II trauma centers
Outcomes	Mortality
Notes	Crew configurations not described
Risk of bias
Bias	Authors' judgement	Support for judgement
Reporting bias	High risk	6/11
External validity	Low risk	3/3
Internal validity	High risk	3/7
Internal validity: confounding and selection bias	High risk	2/6
Power	High risk	0/5