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Table 1 Characteristics of the study subjects and their mammographic features

From: The spatial distribution of radiodense breast tissue: a longitudinal study

   Percent density group at left exit mammogram
  Number of women < 20% (n = 41) 20 to 39% (n = 43) 40 to 59% (n = 38)a 60 to 79% (n = 38)b ≥ 80% (n = 5) All women
Characteristic        
   Entry screen age (years) 164 40.6 (0.8) 40.6 (0.8) 40.7 (1.0) 40.4 (0.8) 41.4 (1.1) 40.6 (0.9)
   Exit screen age (years) 165 48.6 (1.3) 48.6 (1.5) 48.4 (2.1) 48.9 (1.8) 48.5 (1.7) 48.6 (1.7)
   Height (m) 164 1.6 (0.1) 1.6 (0.1) 1.6 (0.1) 1.6 (0.1) 1.7 (0.1) 1.6 (0.1)
   Weight (kg) 163 77.3 (13.7) 67.1 (11.9) 63.0 (12.6) 58.8 (7.6) 54.2 (8.2) 66.4 (13.6)
   Body mass index (kg/m2) 162 29.1 (4.9) 25.5 (4.1) 23.7 (4.1) 22.0 (2.6) 19.9 (1.8) 25.1 (4.8)
   Age at first birth (years) 138 24.8 (5.1) 25.3 (5.1) 27.2 (4.9) 27.4 (4.3) 27.7 (7.8) 26.1 (5.0)
   Number of births        
0 27 (16.4) 6 (14.6) 4 (9.3) 6 (15.8) 9 (23.7) 2 (40.0)  
1 18 (10.9) 4 (9.8) 7 (16.3) 4 (10.5) 1 (2.6) 2 (40.0)  
2 79 (47.9) 19 (46.3) 22 (51.2) 19 (50.0) 18 (47.4) 1 (10.0)  
3+ 41 (24.9) 12 (29.3) 10 (23.3) 9 (23.7) 10 (26.3) 0 (0.0)  
Mammographic features        
   Entry screen, left breast        
Total breast area (cm2) 164 168.8 (70.0) 123.6 (32.9) 111.8 (43.7) 100.2 (29.4) 106.4 (48.3) 126.3 (53.2)
Dense area (cm2) 164 16.3 (13.0) 38.8 (19.4) 52.1 (22.4) 61.7 (20.9) 80.1 (32.2) 42.8 (26.5)
Lucent area (cm2) 164 152.5 (76.8) 84.8 (33.9) 59.6 (36.2) 38.5 (20.7) 26.3 (17.3) 83.5 (63.6)
Percent density (%) 164 13.0 (13.4) 32.6 (15.5) 48.0 (15.4) 62.5 (13.3) 76.9 (5.6) 39.5 (23.9)
Exit screen, left breast        
   Total breast area (cm2) 165 194.0 (76.3) 144.6 (44.1) 119.1 (40.6) 105.6 (30.9) 102.1 (37.0) 140.7 (60.8)
   Dense area (cm2) 165 16.6 (10.3) 42.3 (14.3) 55.2 (17.7) 69.8 (19.7) 83.7 (28.9) 46.5 (25.9)
   Lucent area (cm2) 165 177.5 (77.1) 102.3 (34.1) 63.9 (25.0) 35.8 (12.6) 18.4 (8.2) 94.3 (69.7)
   Percent density (%) 165 9.6 (6.1) 29.7 (5.5) 47.0 (5.8) 66.4 (4.4) 82.5 (1.8) 38.7 (22.7)
  1. Data presented as mean (standard deviation) or n (%). aThere were 37 women at entry and 38 women at exit; weight and body mass index are missing for one woman in this group. bHeight and weight missing for one woman (each); body mass index missing for two women in this group.