Frequencies for a2 variable in midrvacc dataset :

         a2 |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 |        284       61.21       61.21
          1 |          1        0.22       61.42
          2 |          5        1.08       62.50
          3 |          4        0.86       63.36
          4 |          3        0.65       64.01
          5 |          2        0.43       64.44
          6 |          2        0.43       64.87
          7 |          5        1.08       65.95
          8 |          7        1.51       67.46
          9 |          6        1.29       68.75
         10 |          7        1.51       70.26
         11 |         10        2.16       72.41
         12 |         10        2.16       74.57
         13 |          5        1.08       75.65
         14 |         11        2.37       78.02
         15 |         11        2.37       80.39
         16 |          8        1.72       82.11
         17 |          8        1.72       83.84
         18 |          2        0.43       84.27
         19 |         13        2.80       87.07
         20 |          7        1.51       88.58
         21 |          4        0.86       89.44
         22 |          8        1.72       91.16
         23 |          5        1.08       92.24
         24 |          3        0.65       92.89
         25 |          3        0.65       93.53
         26 |          4        0.86       94.40
         27 |          3        0.65       95.04
         28 |          7        1.51       96.55
         29 |          4        0.86       97.41
         30 |          2        0.43       97.84
         31 |          5        1.08       98.92
         32 |          2        0.43       99.35
         34 |          1        0.22       99.57
         36 |          1        0.22       99.78
         39 |          1        0.22      100.00
------------+-----------------------------------
      Total |        464      100.00

by Jean Roth , jroth@nber.org , 18 Apr 2016