                                       
    time  1  2  3  4  5  6  7  8  9  10
 subject X1 X2 X3 X4 X5 X6 X7 X8 X9 X10
       3  0  0  0  0  0  0  0  0  0  NA
      10  0  0  0  0  0  0  0  0  0   0
      15  0  0  0  0  5  0  0  0  0   0
      16  0  0  0  0  0  0  0  1  0   0
      19  0  0  0  0  0  0  0  0  0   0
      31  0  0  0  0  0  0  0  0 NA   0
      51  0  0  0  0  0  0  0  0  0   0
      52  0  0  0  0  0  0  0  0  0   0
      63  0  0  0  0  0  0  0  0  0   0
      78  0  0  0  0  0  0  0  0  0   0
      79  0  0  0  0  0  0  1  2  0  NA
      86  0  0  0  0  0  0  0  0 NA   0
