Frequencies for first 10,000 rows of urf_hydra variable in natl2003 dataset :

Hydramnios/ |
Oligohydram |
     nios U |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |        186        1.86        1.86
          2 |      8,992       89.92       91.78
          8 |          7        0.07       91.85
          9 |        815        8.15      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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