person sex y1   y2   y3   y4
 1      F  21.0 20.0 21.5 23.0
 2      F  21.0 21.5 24.0 25.5
 3      F  20.5 24.0 24.5 26.0
 4      F  23.5 24.5 25.0 26.5
 5      F  21.5 23.0 22.5 23.5
 6      F  20.0 21.0 21.0 22.5
 7      F  21.5 22.5 23.0 25.0
 8      F  23.0 23.0 23.5 24.0
 9      F  20.0 21.0 22.0 21.5
10      F  16.5 19.0 19.0 19.5
11      F  24.5 25.0 28.0 28.0
12      M  26.0 25.0 29.0 31.0
13      M  21.5 22.5 23.0 26.5
14      M  23.0 22.5 24.0 27.5
15      M  25.5 27.5 26.5 27.0
16      M  20.0 23.5 22.5 26.0
17      M  24.5 25.5 27.0 28.5
18      M  22.0 22.0 24.5 26.5
19      M  24.0 21.5 24.5 25.5
20      M  23.0 20.5 31.0 26.0
21      M  27.5 28.0 31.0 31.5
22      M  23.0 23.0 23.5 25.0
23      M  21.5 23.5 24.0 28.0
24      M  17.0 24.5 26.0 29.5
25      M  22.5 25.5 25.5 26.0
26      M  23.0 24.5 26.0 30.0
27      M  22.0 21.5 23.5 25.0