Fig. 1From: Outcomes after helicopter versus ground emergency medical services for major trauma--propensity score and instrumental variable analyses: a retrospective nationwide cohort studyStudy Flow Diagram Detailing the Stratification and Selection of Patients in the JTDB (2004–2014). JTDB indicates Japan Trauma Data Bank; ISS, injury severity score; HEMS, helicopter emergency medical services; GEMS, ground emergency medical serviceBack to article page