Table II.

Information content by match variable

	Information Content (bits) PHIS	Information Content (bits) NTDB	t-test P
Administrative variables
Demographics
Age (years)	4.07	4.09
Admission year	1.98	1.95
Discharge year	1.99	1.96
Gender	0.96	0.94
Insurance type	1.42	1.38
Race/ethnicity	1.61	1.59
Hospital Course
ICU admission (yes/no)	0.59	0.59
Hospital length of stay	2.75	2.48
Discharge disposition	0.35	0.31
Hospital (estimated iteratively)	1.79	1.79
Administrative Total	17.51	17.08
Administrative bits per variable	1.75	1.71	0.93
ICD-9-CM variables
Injury Severity
Injury Mechanism	2.59	2.30
Injury Severity Score (ISS)	2.83	2.95
Body region AIS scores
Head	1.06	1.45
Face	0.70	0.85
Neck	0.05	0.06
Chest	0.35	0.43
Abdomen/Pelvis	0.56	0.67
Spine	0.23	0.34
Upper Extremity	1.05	1.18
Lower Extremity	1.09	1.12
External, Burns, Other	0.48	0.41
Injury Type (yes/no)
Abuse/Assault	0.31	0.35
Amputation	0.04	0.06
Blood Vessel	0.05	0.07
Burns	0.29	0.25
Dislocation	0.12	0.12
Fracture	0.99	0.96
Internal Organ	0.64	0.82
Nerve	0.08	0.08
Open Wound	0.58	0.71
Sprain/Strain	0.12	0.18
System wide and late effects	0.12	0.05
Procedures (yes/no)
Arterial catheter placement	0.12	0.07
Chest tube placement	0.06	0.05
Closed reduction/Internal fixation	0.49	0.58
Closed reduction/No fixation	0.31	0.41
CVC placement	0.27	0.23
Craniotomy or craniectomy	0.06	0.08
Gastrostomy tube placement	0.10	0.03
ICP monitor placement	0.09	0.08
Intubation	0.19	0.14
Mechanical ventilation < 96 hours	0.22	0.08
Mechanical ventilation ≥ 96 hours	0.19	0.05
Open reduction/Internal fixation	0.42	0.44
Open reduction/No fixation	0.04	0.04
Tracheostomy	0.04	0.02
Splint placement	0.09	0.27
Wound closure	0.24	0.32
Wound debridement	0.26	0.24
ICD-9-CM Total	17.52	18.54
ICD-9-CM bits per variable	0.45	0.48	0.85