TABLE 3.

Population attributable risks for postmenopausal invasive breast cancer, Wisconsin, Massachusetts, and New Hampshire, 1997–2001

Risk factor	Summary PAR *		Individual PAR
	PAR%†	95% CI*	PAR%†	95% CI
Factors not modifiable after menopause	57.3	47.5, 65.4
Reproductive and menstrual factors	42.2	30.7, 51.8
Age at menarche			18.8	7.9, 29.0
Age at menopause			13.7	6.6, 19.6
Age at first full-term pregnancy‡			5.2	−3.2, 13.9
Parity			13.3	6.9, 19.8
First-degree family history of breast cancer			8.5	6.5, 10.5
Personal history of benign breast disease			9.7	7.3, 12.0
Height at age 25 years			11.0	3.5, 18.5
Factors modifiable after menopause	40.7	23.0, 55.1
Current postmenopausal hormone use§			4.6	−3.5, 11.9
Recent alcohol consumption (past year)			6.1	2.1, 10.3
Weight gain since age 18 years¶			21.3	13.1, 29.3
Recent recreational physical activity#			15.7	−6.5, 33.7

^*PAR, population attributable risk; CI, confidence interval.

^†Assumes all participants move to the lowest risk category of factor or combination of factors, while other variables are held constant. For participants missing data for a variable, assumes no change in risk according to that variable. Adjusted for age, state of residence, weight at age 18 years, screening mammograms per year over the last 5 years, and all variables in tables 1 and 2.

^‡Among parous women only.

^§Assumes no change in risk for never users.

^¶Assumes no change in risk for women who lost more than 5 kg.

^#Averaged over the period 6 years to 1 year prior to the participant's reference date.