Table 3. Univariate analysis of risk factors for occult pneumothorax in supine chest radiography according to injury score.

Chest radiography	All (n=1,284)				AIS <2 (n=114)				AIS ≥3 (n=1,170)
	OP−	OP+	P		OP−	OP+	P		OP−	OP+	P
Rib fracture			<0.001				0.512				<0.001
Negative	233	188			25	56			208	132
Positive	368	495			13	20			355	475
Subcutaneous emphysema			<0.001				1.000				<0.001
Negative	549	465			34	67			515	398
Positive	52	218			4	9			48	209
Lung contusion			<0.001				0.454				<0.001
Negative	399	388			29	63			370	325
Positive	202	295			9	13			193	282
Pneumomediastinum			0.099				–				0.093
Negative	598	673			38	76			560	597
Positive	3	10			0	0			3	10

Data are presented as numbers. AIS, abbreviated injury score; OP, occult pneumothorax.