Table 2.

Demographic Characteristics and Distribution of Risk Factors for Breast Cancer in Participants, by Study Stage, Shanghai Breast Cancer Study, 1996–2005

Characteristic	Stage 1 (SBCS I; 1996–1998)					Stage 2 (SBCS II; 2002–2005)					SBCS I and SBCS II Combined
	Cases(n = 1,144)		Controls(n = 1,256)		P Value	Cases (n = 1,918)		Controls (n = 1,819)		P Value	Cases (n = 3,062)		Controls (n = 3,075)		P Value
	Mean (SD)	%	Mean (SD)	%		Mean (SD)	%	Mean (SD)	%		Mean (SD)	%	Mean (SD)	%
Demographic factors
Age, years	47.6 (8.0)		47.2 (8.7)		0.227	50.9 (8.3)		51.7 (8.3)		0.002	49.7 (8.3)		49.9 (8.8)		0.317
Educational level of high school or more		43.4		42.8	0.763		57.4		47.7	<0.001		52.2		47.6	<0.001
Postmenopausal		33.0		36.0	0.132		43.6		49.7	<0.001		39.7		44.1	<0.001
Reproductive risk factors for breast cancer
Age at menarche, years	14.5 (1.6)		14.7 (1.7)		<0.001	14.4 (1.7)		14.7 (1.8)		<0.001	14.4 (1.7)		14.7 (1.8)		<0.001
Age at menopausea, years	48.2 (4.6)		47.5 (4.9)		0.038	48.5 (4.4)		48.3 (4.6)		0.231	48.4 (4.4)		48.0 (4.7)		0.023
Age at first livebirth, years	26.8 (4.1)		26.2 (3.8)		<0.001	26.3 (3.6)		25.7 (3.8)		<0.001	26.5 (3.8)		25.9 (3.8)		<0.001
No. of livebirthsb	1.5 (0.8)		1.5 (0.9)		0.191	1.2 (0.7)		1.4 (0.8)		<0.001	1.3 (0.7)		1.4 (0.8)		<0.001
Prior hormone replacement therapy		2.5		2.6	0.989		4.3		3.1	0.053		3.6		2.9	0.070
Other risk factors breast cancer
Family history of breast cancer		3.3		2.4	0.177		5.4		3.1	<0.001		4.6		2.8	<0.001
History of fibroadenoma		9.4		5.2	<0.001		10.1		5.6	<0.001		9.9		5.4	<0.001
Body mass indexc	23.6 (3.4)		23.2 (3.4)		0.013	23.7 (3.3)		23.4 (3.2)		0.004	23.7 (3.3)		23.3 (3.3)		<0.001
Waist-to-hip ratio	0.81 (0.1)		0.80 (0.1)		<0.001	0.83 (0.1)		0.82 (0.1)		<0.001	0.82 (0.1)		0.81 (0.1)		<0.001
Physical exercised		19.3		26.1	<0.001		29.3		34.1	0.002		25.6		30.8	<0.001

Abbreviations: SBCS, Shanghai Breast Cancer Study; SD, standard deviation.

^aAmong postmenopausal women.

^bAmong parous women.

^cWeight (kg)/height (m)².

^dSelf-reported regular leisure-time physical activity (any vs. none).