Table 2.

Estimated Risk of Lung Cancer Among Women by Parity, Lung Cancer Susceptibility Study, Boston, Massachusetts, 1992–2004

Analysis and Parity	Cases		Controls		Age-Adjusted		Multivariate-Adjusteda		P Value
	No.	%	No.	%	OR	95% CI	OR	95% CI
Dichotomous analysis (n = 1,852)b	(n = 1,004)		(n = 848)
0 (nulliparous)	149	15	117	14	1	Referent	1	Referent
≥1	855	85	731	86	0.74	0.56, 0.99	0.71	0.52, 0.97	0.03
Categorical analysis (n = 1,451)c	(n = 672)		(n = 779)
0 (nulliparous)	117	17	110	14	1	Referent	1	Referent
1	85	13	84	11	0.97	0.63, 1.49	0.97	0.59, 1.60
2	160	24	214	27	0.69	0.48, 0.98	0.75	0.50, 1.13
3	136	20	194	25	0.56	0.39, 0.81	0.52	0.35, 0.79
≥4	174	26	177	23	0.64	0.45, 0.92	0.57	0.38, 0.85	0.0003d

Abbreviations: CI, confidence interval; OR, odds ratio.

^aAdjusted for age (years), smoking status (current, former, or never smoker), pack-years of smoking, and years since quitting smoking.

^bIncluded cases and controls enrolled in the study between 1992 and 2004.

^cIncluded cases and controls enrolled in the study between 1992 and 2002.

^dP value from a test for linear trend with adjustment for age, smoking status, pack-years of smoking, and years since quitting smoking.