Frequencies for first 10,000 rows of urf_hydra variable in natlterr2005 dataset :

Hydramnios/ |
Oligohydram |
     nios U |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         32        0.32        0.32
          2 |      4,436       44.36       44.68
          9 |      1,787       17.87       62.55
          . |      3,745       37.45      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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