Frequencies for first 10,000 rows of urf_hydra variable in natl2005 dataset :

Hydramnios/ |
Oligohydram |
     nios U |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |        172        1.72        1.72
          2 |      9,705       97.05       98.77
          9 |        123        1.23      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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