Table 2. Odds ratio (OR) for confirmed NEC in infants exposed to feeding advancement and PRBC transfusion 48 hours prior to NEC onset.

	A	B	C	D	OR (95% CI) a
Feed fortification	5	10	6	11	1.67 (0.61, 4.59)
Increase in feeding volume	19	10	16	9	0.63 (0.28, 1.38)
PRBC transfusion	4	9	5	20	1.80 (0.60, 5.37)

Abbreviations: NEC, necrotizing enterocolitis; PRBC, packed red blood cells

A: Number of concordant pairs exposed in both hazard and control period (n₁₁)

B: Number of discordant pairs exposed in hazard period, unexposed in control period (n₁₀)

C: Number of discordant pairs unexposed in hazard period, exposed in control period (n₀₁)

D: Number of concordant pairs unexposed in both hazard and control period (n₀₀)

^a OR defined as B/C or n₁₀/ n₀₁