Appendix Table 1.
The following characteristics were included in imputation models to multiply impute values for those characteristics that were missing for one or more patients. | ||||
---|---|---|---|---|
In analysis models? | Characteristic | Modeled as ... | # Missing | Imputation method |
Y | 28-day mortality | Indicator | 0 | |
Y | EMS Time (minutes)a | Categorical: ≤30, 30-45, 46-60, >60 | 0 | |
Y | Age | Continuous, spline with knot at 45 years | 1 | PMM |
Y | Male gender | Indicator | 0 | |
Y | Penetrating injury | Indicator | 0 | |
Y | ISSb | Continuous | 31 | PMM |
Y | Qualifying SBP | Categorical: ≤50, 51-60, 61-70, 71-80, 81-90 | 0 | |
Y | Highest heart rate (beats/minute) | Categorical: <50, 51-110, >110 | 4 | ML |
Y | Initial GCS | Continuous | 1 | PMM |
Y | Out-of-hospital advanced airway attempted | Indicator | 0 | |
Y | Air transport | Indicator | 0 | |
Y | Regional site | Categorical - fixed effect | 0 | |
N | Required critical intervention | Indicator | 0 | |
N | ISS disposition category | Categorical: Died < 6 hrs, other death, discharge ≥ 2 days, discharge < 2 days, discharge from ED, unknown | 1 | ML |
N | Serious injury (AIS ≥ 3) to chest or abdomen | Indicator | 4 | LR |
N | Serious injury (AIS ≥ 3) to extremity | Indicator | 7 | LR |
N | Serious injury (AIS ≥ 3) to the head | Indicator | 1 | LR |
Abbreviations: AIS, Abbreviated Injury Score; ED, emergency department; GCS, Glasgow Coma Scale; ISS, Injury Severity Score; LR, logistic regression; ML, multinomial logit; PMM, predictive mean modeling; SBP, systolic blood pressure.
EMS time is also used as a continuous variable in some analysis models but not in the imputation models.
In most instances ISS is missing because one of the individual AIS scores is listed as “not otherwise specified” preventing the calculation of the ISS. However, there are other AIS scores available and this information can be used in the imputation process (see last 5 characteristics).