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Table 1 Descriptive characteristics of study population (n = 1121) at the time of mammography, Nurses' Health Study (1989–1998)

From: Breast cancer susceptibility loci and mammographic density

Characteristic   
Mean values Mean SD
Age, y 58.4 7.3
Body mass index, kg/m2 25.6 4.6
Percentage mammographic density, % 27.1 20.6
Frequencies a N %
Menopausal/hormone status   
   Premenopausal 217 19.4
   Postmenopausal/never user 371 33.1
   Postmenopausal/past user 317 28.3
   Postmenopausal/current user 216 19.3
Alcohol consumption   
   None 327 31.8
   <5 g/day 346 33.6
   5 to 14.9 g/day 221 21.5
   15+ g/day 135 13.1
Parity/age at first birth   
   Nulliparous 83 7.5
   Parous/<25 years 549 49.6
   Parous/25 to 29 years 382 34.5
   Parous/>30 93 8.4
Prior benign breast disease 465 41.5
Family history of breast cancer 135 12.0
  1. a Numbers may not be added to total due to missing data.