Pre-Post Data Example
 MTB > describe c1-c2
 
                 N     MEAN   MEDIAN   TRMEAN    STDEV   SEMEAN
 C1             20    25.80    27.00    26.28     6.30     1.41
 C2             20    28.30    27.50    28.61     5.95     1.33
 
               MIN      MAX       Q1       Q3
 C1          10.00    33.00    22.25    31.00
 C2          15.00    36.00    26.00    33.75
 
 MTB > let c3 = c2 - c1
 MTB > describe c3
 
                 N     MEAN   MEDIAN   TRMEAN    STDEV   SEMEAN
 C3             20    2.500    3.000    2.778    2.893    0.647
 
               MIN      MAX       Q1       Q3
 C3         -6.000    6.000    1.000    5.250
 
 MTB > stem c3
 
 Stem-and-leaf of C3        N  = 20
 Leaf Unit = 1.0

     1   -0 6
     1   -0 
     1   -0 
     2   -0 0
     6    0 0011
    (9)   0 222333333
     5    0 
     5    0 66666
 
 MTB > boxplot c3 
 
                                           ---------------
               *                       ----I       +     I------
                                           ---------------
           --------+---------+---------+---------+---------+--------C3      
                -5.0      -2.5       0.0       2.5       5.0
 
 MTB > tinterval 90 c3 
 
              N      MEAN    STDEV  SE MEAN   90.0 PERCENT C.I.
 C3          20     2.500    2.893    0.647  (   1.381,   3.619)
 
 MTB >  
 MTB > tinterval 99 c3
 
              N      MEAN    STDEV  SE MEAN   99.0 PERCENT C.I.
 C3          20     2.500    2.893    0.647  (   0.649,   4.351)
 
 
