obs  y      x
1  21.67  71.5
2  23.36  79.0
3  21.55  83.2
4  20.87  77.8
5  22.49  80.0
6  22.71  82.5
7  25.52  82.0
8  23.03  76.8
9  20.24  68.5
10 24.10  77.5
11 23.64  81.9
12 23.45  82.6
13 24.41  85.0
14 24.08  85.6
15 23.45  78.0
16 23.51  82.0
17 25.26  88.3
18 23.80  73.6
19 24.19  78.5
20 27.73  87.3