Inclusion and exclusion criteria

A total of 35,214,824 persons were involved in all EMS activations. All road crashes were selected. Crashes were identified using the International Classification of Disease (ICD) code, version 10 (Figure 1). Specifically, cases identified as ICD V01‐V89 were selected. These cases represented crashes involving pedestrians (V01‐V09), pedal cyclists (V10‐V19), motorcycle (V20‐V29), 3‐wheeled motor (V30‐V39), cars (V40‐V49), trucks (V50‐V59), heavy transport vehicle (V60‐V69), bus (V70‐V79), and other land transport (V80‐V89) (n = 674,365). Cases whose crash outcome was classified as “canceled” were excluded (n = 1,532). Also, we excluded cases whose crash response times were over 1 hour (n = 1,266). These cases were excluded because they represent outliers cases that occurred during unique situations. For example, a crash event in Alabama that occurred on March 3 had a response time of 6 hours but the event occurred during a tornado that involved 41 locations. ²⁵ The NEMSIS did not provide context for all the unexpectedly prolonged response times so we excluded cases whose response time exceeded 1 hour. Additionally, we excluded cases with missing crash notification to EMS base station departure time (n = 3,963) and missing EMS base station departure time to crash scene arrival time (2,523). Also, we excluded cases when the predictor and control variables have missingness less than 1% (n = 10,466). The final sample included 654,675 persons involved in all forms of road crashes.

Data selection steps