Frequencies for first 10,000 rows of urf_hydra variable in natlterr2003 dataset :

Hydramnios/ |
Oligohydram |
     nios U |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |        108        1.08        1.08
          2 |      9,867       98.67       99.75
          8 |         23        0.23       99.98
          9 |          2        0.02      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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