Frequencies for first 10,000 rows of hydra variable in natl1990 dataset :

Hydramnios/ |
Oligohydram |
       nios |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         70        0.70        0.70
          2 |      9,881       98.81       99.51
          8 |          1        0.01       99.52
          9 |         48        0.48      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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