Table 3.

Racism and Lifetime Experiences and risk of preterm birth, Baltimore, Maryland 2001–04: interaction models

Model terms	Stratum	Total births	Per cent preterm	Racism HR unadjusted	Interaction P-value	Racism HR adjusteda	Interaction P-value
Two way interactions: individual models
Racism, Stress,	Lower stress	610	15.7%	0.88 [0.59, 1.32]	Racism*Stress	0.92 [0.61,1.38]	Racism*Stress
Racism*Stressb	High stress	220	19.5%	1.29 [0.83, 2.01]	P = 0.41	1.30 [0.83, 2.04]	P = 0.30
Racism, CES-D,	High CES-D	351	19.9%	1.41 [0.93, 2.14]	Racism*CES-D	1.40 [0.92, 2.14]	Racism*CES-D
Racism*CES-Dc	Lower CES-D	481	14.3%	0.71 [0.43, 1.15]	P = 0.07	0.70 [0.42, 1.14]	P = 0.04
Two way interactions: joint model
Racism, Stress, CES-D	High stress, high CES-D	182	18.7%	1.43 [0.90, 2.30]	LR interaction test	1.47 [0.91, 2.39]	LR interaction test
Racism*Stress					P = 0.19		P = 0.10
	High stress, lower CES-D	42	21.4%	0.74 [0.38, 1.45]		0.79 [0.40, 1.57]
Racism*CES-Da					Racism*Stress		Racism*Stress
	Lower stress, high CES-D	177	20.3%	1.35 [0.80, 2.29]	P = 0.96	1.34 [0.78, 2.29]	P = 0.54
					Racism*CES-D		Racism*CES-D
	Lower stress, lower CES-D	445	13.5%	0.70 [0.43, 1.14]		0.72 [0.43, 1.20]
					P = 0.12		P = 0.12
Two- and three-way interactions: joint model
Racism, Stress, CES-D	High stress, high CES-D	182	18.7%	1.29 [0.78, 2.12]	LR interaction test	1.32 [0.79, 2.20]	LR interaction test
Racism*Stress					P = 0.10		P = 0.05
Racism*CES-D	High stress, lower CES-D	42	21.4%	1.37 [0.58, 3.23]	Racism*Stress	1.51 [0.64, 3.57]	Racism*Stress
Racism*Stress*CES-Da					P = 0.18		P = 0.08
	Lower stress, high CES-D	177	20.3%	1.56 [0.92, 2.63]	Racism*CES-D	1.55 [0.90, 2.64]	Racism*CES-D
					P = 0.03		P = 0.04
	Lower stress, lower CES-D	445	13.5%	0.61 [0.36, 1.04]	Racism*Stress*CES-D	0.63 [0.36, 1.08]	Racism*Stress*CES-D
					P = 0.07		P = 0.06

^aAdjusted for cigarette smoking second trimester and high locus of control.

^bAdjusted for second trimester cigarette smoking.

^cAdjusted for locus of control.

Racism: Racism Life Experiences scale, above median racism experiences is exposure.

CES-D: Center for Epidemiologic Studies Depressive symptoms scale, score ≥ 16 is exposure.

Stress: Hassles scale, top quartile of stress is exposure.

LR interaction test P-value: compares model with interaction(s) to model with main effects only.

HR: hazard ratio; LR: likelihood ratio.