Table 2. Model Input Assumptions.
| Variable | Base Case Value | Sensitivity Analysis Range | Distribution | Source |
|---|---|---|---|---|
| Cohort characteristics | ||||
| Age, mean, y | 47 | NA | Normal | NTDB |
| Injury Severity Score >15, % | 20.46 | 5-50 | Beta | NTDB |
| Length of stay, d | 3 | 1-14 | Log normal | NTDB |
| Transport | ||||
| Probability of HEMS transport under current practice strategy | 0.165 | 0.10-0.20 | Triangular | NTDB |
| Probability of HEMS transport under AMPT strategy | 0.095 | 0.05-0.15 | Triangular | NTDB |
| Transport distance, miles | 55 | 25-85 | Triangular | Brown et al |
| Probability of fatal HEMS crash per mile traveled | 0.00000016 | 0.000000016-0.0000016 | Triangular | Blumen and Lees |
| Probability of fatal GEMS crash per mile traveled | 0.00000008 | 0.000000008-0.0000008 | Triangular | Levick |
| Costs, $ | ||||
| HEMS service charge per patient | 7172.37 | 4000-10 000 | Triangular | CMS ambulance fee schedule |
| GEMS service charge per patient | 1048.99 | 500-1500 | Triangular | CMS ambulance fee schedule |
| Cost of hospitalization | 58 172 | 15 000-100 000 | Normal | NSCOT |
| Cost of health care within 1 y after injury | 36 593 | 7000-50 000 | Normal | NSCOT |
| Cost of health care >1 y after injury | CMS annual expenditures | 6000-50 000 | Triangular | Delgado et al |
| Crash sequelae | ||||
| Vehicle cost of GEMS crash, $ | 144 900 | 129 900-169 900 | Triangular | Retail web site |
| Vehicle cost of HEMS crash, $ | 4.6 million | 3.2 million-5.5 million | Triangular | Airbus helicopters and bell helicopters |
| QALYs lost in GEMS crash | 30 | 10-50 | Uniform | Delgado et al |
| QALYs lost in HEMS crash | 120 | 30-200 | Uniform | Delgado et al |
| Outcomes | ||||
| Probability of in-hospital survival for patients transported by GEMS | 0.9520 | 0.80-0.98 | Beta | NTDB |
| Probability of in-hospital survival for patients transported by HEMS assigned using AMPT strategy | 0.9566 | 0.85-0.99 | Beta | NTDB |
| Probability of in-hospital survival for patients transported by HEMS assigned using current practice strategy | 0.9556 | 0.85-0.99 | Beta | NTDB |
| Probability of surviving 1 y after discharge alive | 0.97 | 0.95-0.99 | Beta | MacKenzie et al |
| Utility during hospitalization | 0.3 | 0.1-0.7 | Triangular | Assumed |
| Utility discharged alive | 0.6 | 0.5-0.7 | Normal | Delgado et al |
| Utility 1 y after injury | 0.7 | 0.6-0.8 | Normal | NSCOT; Delgado et al |
| Annual probability of mortality >1 y after injury | US annual life tables | NA | NA | CDC; Delgado et al |
| Annual utility >1 y after injury | Health and activity limitation index | 0.55-0.75 | Normal | Gold et al; NSCOT |
| Model variables | ||||
| Discount rate, % | 3 | NA | NA | Weinstein et al |
| Cycle length, y | 1 | NA | NA | NA |
Abbreviations: AMPT, Air Medical Prehospital Triage; CDC, US Centers for Disease Control and Prevention; CMS, US Centers for Medicare and Medicaid Services; GEMS, ground emergency medical services; HEMS, hospital emergency medical services; NA, not applicable; NSCOT, National Study on the Costs and Outcomes of Trauma; NTDB, National Trauma Databank; QALY, quality-adjusted life-years.