Table 1.

Selected characteristics of the women with breast cancer and controls

Characteristic	Cases (n=2282)	Controls (n=2424)
Continuous variables: mean
Age (years)	50.9	50.4
Age at menarche (years)	12.4	12.4
Age at menopause among menopausal women (years)	47.2	45.5
Age at first term pregnancy among parous women (years)a	22.7	22.6
Number of term pregnanciesa	2.1	2.3
Body mass index at reference date minus 5 yearsb	26.1	26.3
Categorical variables: percentc
White race	62.3	61.3
Menopausal status
Pre- or perimenopausal	40.7	40.2
Postmenopausal	39.2	38.0
Unable to classify	20.1	21.8
Family history of breast cancerd
No	78.5	87.1
Yes	17.6	9.0
Adopted or unknown	3.9	3.9
Ever use of hormone replacement therapy	38.0	41.2

^aFor the purposes of this study, term pregnancy was defined as a gestation of at least 27 weeks; if a woman was pregnant at the time of the interview, that pregnancy was not counted.

^bThe body mass index was calculated as the weight in kilograms divided by the square of the height in meters. The reference date was the date of the diagnosis for women with breast cancer and the date of telephone screening for controls.

^cPercentages calculated with nonmissing values.

^dA family history of breast cancer was defined as breast cancer in the woman’s mother, sister or daughter.