Baxt 1983.

Methods	Retrospective cohort, ground comparison group only
Participants	People with blunt trauma only in San Diego, USA, over a 30‐month period
Interventions	HEMS vs. GEMS transport to a trauma center
Outcomes	Mortality
Notes	HEMS crews: physician and nurse, GEMS crews: paramedic and EMT
Risk of bias
Bias	Authors' judgement	Support for judgement
Reporting bias	Low risk	8/11
External validity	Low risk	3/3
Internal validity	Unclear risk	4/7
Internal validity: confounding and selection bias	High risk	3/6
Power	High risk	0/5