Data on mental state of 50 schizophrenia patients.
   
   For each patient, a PANSS (Positive And Negative Symptom Scale)
   score was obtained in weeks 0, 1, 2, 4, 6, 8 following recruitment
   to a trial of a novel form of medication. A reduction in the PANSS
   score represents an improvement in the patient's mental state.

   Entries NA represent missing values of the PANSS score following that
   patient's premature withdrawal from the trial. 

   Columns are:
      y0: PANSS score at week 0
      y1: PANSS score at week 1
      y2: PANSS score at week 2
      y4: PANSS score at week 4
      y6: PANSS score at week 6
      y8: PANSS score at week 8