Table 1.

Baseline Characteristics in 1988 of Women in the Nurses’ Health Study With Use of Screening Mammography in 1988–1990, Crude and Weighted by Inverse Probability of Screening Mammography^a

	Unweighted					Weighted
	No Mammogram (n = 8,558)		Screening Mammogram (n = 34,754)		P Value	No Mammogram (n = 8,558)		Screening Mammogram (n = 34,754)		P Value
	No.	%	No.	%		No.	%	No.	%
Age, years (mean (SD))	54.1 (7.4)		53.9 (7.1)		0.02	53.9 (7.3)		54.0 (7.2)		0.65
Age, years
40–44	1,067	12.5	3,652	10.5	0.022	959	11.1	3,783	10.9	0.72
45–49	1,639	19.2	7,355	21.2		1,801	20.7	7,202	20.8
50–54	1,628	19.0	7,541	21.7		1,861	21.4	7,340	21.2
55–59	1,665	19.5	6,702	19.3		1,674	19.3	6,691	19.3
60–64	1,874	21.9	6,965	20.0		1,745	20.1	7,058	20.4
65–69	685	8.0	2,539	7.3		651	7.5	2,574	7.4
Menopausal status
Premenopausal	2,880	33.6	11,911	34.5	<0.0001	2,949	33.9	11,903	34.4	0.38
Natural menopause	4,520	52.8	17,290	49.8		4,356	50.1	17,426	50.3
Surgical menopause	1,158	13.5	5,473	15.8		1,385	15.9	5,319	15.4
Hormone therapy (if postmenopausal)
Never	3,550	62.5	9,497	41.7		2,582	45.0	10,422	45.8
Current estrogen + progesterone	207	3.6	3,135	13.8	<0.0001	689	12.0	2,674	11.8	0.60
Current estrogen only	573	10.1	4,009	17.6	<0.0001	939	16.4	3,667	16.1	0.68
Current other	144	2.5	1,471	6.5	<0.0001	330	5.8	1,293	5.7	0.85
Past estrogen + progesterone	92	1.6	625	2.8	<0.0001	149	2.6	573	2.5	0.75
Past estrogen only	537	9.5	1,890	8.3	0.005	513	8.9	1,950	8.6	0.37
Past other	575	10.1	2,136	9.4	0.088	540	9.4	2,166	9.5	0.77
Parity
None	504	5.9	2,047	5.9	0.44	490	5.6	2,045	5.9	0.68
1	684	8.0	2,426	7.0		644	7.4	2,479	7.2
2	2,287	26.7	10,270	29.6		2,507	28.8	10,048	29.0
≥3	5,083	59.4	20,011	57.6		5,049	58.1	20,076	57.9
Age at first birth, years
None	504	5.9	2,047	5.9	0.39	490	5.7	2,045	5.9	0.41
<25	4,103	47.9	16,755	48.2		4,313	49.6	16,681	48.1
25–29	3,116	36.4	12,738	36.6		3,056	35.2	12,683	36.6
≥30	835	9.8	3,214	9.2		832	9.6	3,239	9.4
Body mass index, kg/m2
<25	4,139	48.4	18,668	53.7	<0.0001	4,507	51.9	18,228	52.6	0.23
25–<30	2,010	23.5	8,202	23.6		2,078	23.9	8,172	23.6
≥30	2,409	28.2	7,884	22.7		2,106	24.2	8,248	23.8
Smoking status
Never	3,593	42.0	15,723	45.2	<0.0001	3,894	44.8	15,447	44.6	0.99
Past	2,746	32.1	13,720	39.5		3,264	37.6	13,167	38.0
Current	2,219	25.9	5,311	15.3		1,533	17.6	6,034	17.4
Alcohol use
None	3,359	39.2	11,329	32.6	<0.0001	2,924	33.6	11,750	33.9	0.81
<1 drink/day	3,492	40.8	15,805	45.5		3,901	44.9	15,435	44.6
≥1 drinks/day	1,707	20.0	7,620	21.9		1,867	21.5	7,463	21.5
Physical activity, MET hours/week
<10	4,916	57.4	17,876	51.4	<0.0001	4,618	53.1	18,235	52.6	0.63
10–19	1,542	18.0	7,078	20.4		1,683	19.4	6,888	19.9
≥20	2,100	24.5	9,800	28.2		2,390	27.5	9,525	27.5
Benign breast disease
No	6,513	76.1	20,793	59.8	<0.0001	5,446	62.7	21,847	63.0	0.49
Yes	2,045	23.9	13,961	40.2		3,245	37.3	12,801	37.0
Family history of breast cancer
No	7,913	92.5	30,716	88.4	<0.0001	7,747	89.1	30,901	89.2	0.91
Yes	645	7.5	4,038	11.6		944	10.9	3,747	10.8
Family history of other cancer
No	5,326	62.2	20,787	59.8	<0.0001	5,332	61.4	20,897	60.3	0.08
Yes	3,232	37.8	13,967	40.2		3,359	38.6	13,751	39.7
Multivitamin use
No	5,617	65.6	21,041	60.5	<0.0001	5,348	61.5	21,322	61.5	>0.99
Yes	2,941	34.4	13,713	39.5		3,342	38.5	13,326	38.5
Calcium supplement use
No	5,942	69.4	19,504	56.1	<0.0001	5,089	58.6	20,355	58.8	0.74
Yes	2,616	30.6	15,250	43.9		3,602	41.4	14,293	41.2
Aspirin use
No	7,149	83.5	29,035	83.5	0.98	7,240	83.3	28,939	83.5	0.62
Yes	1,409	16.5	5,719	16.5		1,451	16.7	5,709	16.5
History of hypertension
No	6,387	74.6	25,676	73.9	0.15	6,290	72.4	25,617	73.9	0.003
Yes	2,171	25.4	9,078	26.1		2,400	27.6	9,031	26.1
History of high cholesterol
No	7,073	82.6	26,000	74.8	<0.0001	6,570	75.6	26,449	76.3	0.15
Yes	1,485	17.4	8,754	25.2		2,121	24.4	8,199	23.7
History of cardiovascular disease
No	7,661	89.5	31,153	89.6	0.74	7,745	89.1	31,039	89.6	0.20
Yes	897	10.5	3,601	10.4		946	10.9	3,609	10.4
History of rheumatoid arthritis
No	8,070	94.3	32,884	94.6	0.24	8,221	94.6	32,764	94.6	0.91
Yes	488	5.7	1,870	5.4		470	5.4	1,884	5.4
History of osteoarthritis
No	6,323	73.9	24,575	70.7	<0.0001	6,138	70.6	24,707	71.3	0.21
Yes	2,235	26.1	10,179	29.3		2,553	29.4	9,942	28.7
History of osteoporosis
No	8,216	96.0	32,861	94.6	<0.0001	8,213	94.5	32,855	94.8	0.23
Yes	342	4.0	1,893	5.4		478	5.5	1,794	5.2
History of diabetes
No	8,199	95.8	33,523	96.5	0.004	8,337	95.9	33,368	96.3	0.10
Yes	359	4.2	1,231	3.5		354	4.1	1,280	3.7

Abbreviations: MET, metabolic equivalent; SD, standard deviation.

^aExcludes 1,969 women with mammograms for symptoms.