Table 1.

Prevalence of Smoking at Various Time Periods Indicated by Variables Derived From Interviews, Northern California Childhood Leukemia Study, 1999–2007

Self-reported Cigarette Smoking Variable	Response			Median Nicotine Concentration (ng/g)
	Yes	No	% Yes	Yes	No	P Valuea
Mother ever smoked	137	326	30	465	203	<0.0001
Mother smoked at first interview	41	422	9	1,256	240	<0.0001
Mother smoked during 3 months before conceptionb	53	410	11	1,071	237	<0.0001
Mother smoked during pregnancyb	29	434	6	1,634	245	<0.0001
Mother smoked after birthb	53	409	11	847	235	<0.0001
Father ever smoked	182	277	40	415	184	<0.0001
Father smoked at first interview	76	380	17	774	214	<0.0001
Father smoked during 3 months before conceptionb	95	363	21	613	215	<0.0001
Anyone else smoked during 1 year before birth	25	438	5	1,109	252	<0.0001
Anyone else smoked during 1 year after birth	17	443	4	1,109	255	<0.0001
Anyone smoked in the house during the month before dust collectionb	21	446	4	1,256	256	<0.0001

^aKruskal-Wallis one-way analysis of variance.

^bIndicates that cigarette consumption (cigarettes smoked per day) was obtained for this category.