c1 is method (1 = selective, 2=nonselective)                   
c2 is repeated measure (1=pre, 2=post)                         
c3 is outcome (urea synthesis)                                 
c4 is subject (labelled 1,...ni within each group)             


1 1 51  1
1 2 48  1
1 1 35  2
1 2 55  2
1 1 66  3
1 2 60  3
1 1 40  4
1 2 35  4
1 1 39  5
1 2 36  5
1 1 46  6
1 2 43  6
1 1 52  7
1 2 46  7
1 1 42  8
1 2 54  8
2 1 34  1
2 2 16  1
2 1 40  2
2 2 36  2
2 1 34  3
2 2 16  3
2 1 36  4
2 2 18  4
2 1 38  5
2 2 32  5
2 1 32  6
2 2 14  6
2 1 44  7
2 2 20  7
2 1 50  8
2 2 43  8
2 1 60  9
2 2 45  9
2 1 63  10
2 2 67  10
2 1 50  11
2 2 36  11
2 1 42  12
2 2 34  12
2 1 43  13
2 2 32  13