Appendix Table 2.

Traumatic Brain Injury Cohort: Characteristics in the Imputation and Analysis Models.

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	6-month GOSE ≤ 4	Indicator	185	LR
Y	28-day mortality	Indicator	8	LR
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	ISS^b	Continuous	31	PMM
Y	Head AIS ≥ 3	Indicator	8	LR
Y	Initial SBP	Categorical: ≤90, 91-105, 106-120, 121-180, >180	10	ML
Y	Highest heart rate (beats/minute) > 110	Indicator	2	LR
Y	Qualifying GCS	Continuous	0
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	Discharge GOSE	Continuous	69	PMM
N	Days alive and out of the hospital through day 28; death before 28 days is coded as 0.	Continuous	13	PMM
N	ISS disposition category	Categorical: Died < 6 hrs, other death, discharge ≥ 2 days, discharge < 2 days, discharge from ED, unknown	0	ML
N	Serious injury (AIS ≥ 3) to chest or abdomen	Indicator	0	LR
N	Serious injury (AIS ≥ 3) to extremity	Indicator	0	LR

Abbreviations: AIS, Abbreviated Injury Score; GCS, Glasgow Coma Scale; GOSE, Glasgow Outcome Scale – Extended, 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.