Frequencies for first 10,000 rows of hydra variable in natl2002 dataset :

Hydramnios/ |
Oligohydram |
       nios |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |        171        1.71        1.71
          2 |      9,516       95.16       96.87
          9 |        313        3.13      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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