Table 2. Crude Injury Admission Rate Ratios by Neighborhood Socioeconomic Status Categories in Shelby County, TN, 1996 – 2005 for Blunt and Penetrating Injuries.

Injury	Neighborhood Socioeconomic Status Category
	Lowest n = 634,560 person-years		Low-Middle n = 1,237,690 person-years		Middle n = 1,385,260 person-years		High-Middle n = 1,579,740 person-years		Highest n = 1,500,930 person-years
	No. of admissions	CIRR* (95% CI)	No. of admissions	CIRR (95% CI)	No. of admissions	CIRR (95% CI)	No. of admissions	CIRR (95% CI)	No. of admissions	CIRR
Blunt	2,722	5.74	3,286	3.55	3,017	2.91	2,010	1.70	1,122	Referent
mechanism*		(5.35, 6.15)		(3.32, 3.80)		(2.72, 3.12)		(1.58, 1.83)
Penetrating	1,650	20.98	1,614	10.52	1,083	6.31	529	2.70	186	Referent
mechanism*		(18.03, 24.42)		(9.04, 12.25)		(5.40, 7.37)		(2.29, 3.19)

Crude injury admission rate ratios were calculated in the following manner. First crude injury rates were calculated. The numerator for each rate calculation was the number of injury related admissions from each neighborhood socioeconomic status category to the Presley Memorial Trauma Center from 1996 – 2005. The denominator was the total number of person-years at risk for injury in each neighborhood socioeconomic status category in Shelby County, Tennessee from 1996 – 2005. For crude rate ratio calculations the crude injury rate for the Highest Neighborhood Socioeconomic Status Category was used as the referent.

^*Mechanism of injury was determined from ICD-9 E-codes recorded during hospital admission. Categories for mechanism of injury are reported so that they are consistent with the Centers for Disease Control Injury Intentionality Matrix as published in the MMWR 1997;46:1-30.; 439 persons had missing mechanism of injury information and were excluded from rate calculations.

CIRR, Crude injury admission rate ratio.