Table 1 Characteristics of 52,814 women undergoing digital mammography (first time) between 2003 and 2011

Age (years)^a, median (IQR)

56

(51 ; 63)

59

(54 ; 64)

55

(50 ; 62)

Number of screening rounds participated in, median (IQR)

5

(2 ; 8)

7

(4 ; 9)

4

(2 ; 7)

Follow up (years)^b, median (IQR)

4.2

(2.0 ; 6.2)

3.8

(2.1 ; 4.3)

2.3

(1.3 ; 4.0)

 Category 1

10,458

(20.0)

46

(15.4)

12

(5.4)

 Category 2

21,276

(40.7)

143

(47.8)

72

(32.1)

 Category 3

15,856

(30.3)

89

(29.8)

100

(44.6)

 Category 4

4,701

(9.0)

21

(7.0)

40

(17.9)

 Dense volume (cm³)^a

57.7

(42.8 ; 78.8)

63.2

(49.0 ; 83.5)

67.7

(48.9 ; 93.2)

 Percent dense volume (%)^a

6.4

(4.8 ; 9.8)

6.5

(5.0 ; 9.4)

8.5

(6.2 ; 13.6)

 Nondense volume (cm³)^a

805.0

(518.8 ; 1183.7)

929.1

(585.6 ; 1298.7)

720.3

(469.8 ; 1030.9)

 Total breast volume (cm³)^a

866.8

(573.9 ; 1256.8)

994.0

(648.6 ;1376.5)

797.5

(531.8 ; 1105.8)