Frequencies for first 10,000 rows of hydra variable in natl1997 dataset :

Hydramnios/ |
Oligohydram |
       nios |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |        104        1.04        1.04
          2 |      9,887       98.87       99.91
          9 |          9        0.09      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 22 Dec 2015