Table 4.

Hierarchical Multilevel Analysis of Risk Factors for RF Due to Severe LRTI in Premature Infants^a

Risk factor	Level 1	Level 2	Level 3
	P Value	P Value	P Value
No/incomplete high school education	.023	.2	.107
Age ≤6 months		.009	.031
Underweight		.019	.126
Never breastfed		.03	.558
Apnea			<.001
Pneumonia			.09
Sepsis			<.001
Pneumothorax			.04

Abbreviations: LRTI, lower respiratory track infection; RF, respiratory failure.

^aIn levels 2 and 3 of the hierarchical analysis, the variables analyzed in the previous level were used only to adjust the next level variables (italicized; gray cells). Bold indicates P < .05.