Frequencies for first 10,000 rows of hydra variable in natl1991 dataset :

Hydramnios/ |
Oligohydram |
       nios |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         57        0.57        0.57
          2 |      9,935       99.35       99.92
          8 |          1        0.01       99.93
          9 |          7        0.07      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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