Frequencies for first 10,000 rows of hydra variable in natl1989 dataset :

Hydramnios/ |
Oligohydram |
       nios |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         55        0.55        0.55
          2 |      9,742       97.42       97.97
          9 |        203        2.03      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 3 Jan 2016